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daggerboard (n) – A dagger-shaped board that projects down into the water below a sailboat's hull; its purpose is to help keep the boat on course

danbuoy (n) – A floating safety device thrown off of a boat when a crew member goes overboard; a pole that stands upright in the water, giving a visual reference to the crew as to where the overboard victim is located. It also has a light on top of it for reference at night.

Darwinism (n) – The theory of evolution that states that all plants and animals developed from earlier forms by changing and adapting to their environment for survival

data (n) – Factual information, in the form of measurements, that is used for reasoning discussion or calculation

date (n) – The sweet, fleshy fruit of the date palm, having a large, hard seed

daunting (adj) – Discouraging; fearsome

davit (n) – An upright made of timber or iron, projecting over the side or stern of a ship and used for suspending, hoisting ir lowering a small boat

day watch (n) – The ship’s watch that occurs during the daytime

D-Day (n) – June 6, 1944, the day on which Allied forces invaded Western Europe during World War II

dead ahead (adv) – Directly in front of a vessel

deadeye (n) – A circular block in a ship’s shrouds or stays, used to adjust tension

dead reckoning (n) – The estimation of a ship’s position based on data recorded in the ship's logbook (e.g., speed and time spent on a certain course) rather than more precise measurements (e.g., astronomical observations, radar, GPS, or LORAN)

dearth (n) – A lack of

debris (n) – 1 : In the rainforest, dead vegetation that has fallen to the forest floor  2 : Carelessly discarded refuse or litter  3 : Rough, broken bits of stone, wood, and other materials, often found in a place of destruction

deciduous (adj) – Shedding or losing foliage at the end of the growing season

deciduous (n) – Having leaves that die and fall off at the end of a growth period or season

decimate (v) – To destroy or damage; to reduce markedly in amount

deck (n) – A part of a ship that serves both as a floor and as a full or partial covering for a level of the ship lower than it is

declination (n) – In astronomy, the angular distance to a point on a celestial object measured north or south from the Celestial Equator; expressed in degrees

decompose (v) – To break down, rot or decay

decomposer (n) – Any organism that breaks down the remains of dead animals and plants

decomposition (n) – The breakdown of remains of dead animals and plants by bacteria or fungus

decompression sickness (n) – Also called "the bends", an ailment caused by an excess of dissolved nitrogen in the body; this illness is seen in divers who ascend too quickly to the water’s surface and/or remain too long at great depths underwater

decrepit (adj) – Broken down by age or hard use

defecate (v) – To excrete solid waste

defibrillator (n) – An medical device used to restore normal heartbeat by applying a brief electric shock to the heart

deforestation (n) – The removal of trees and forests from the land

degradable (adj) – Capable of being separated into constituent parts or elements or into simpler compounds

degradation (n) – A worsening of quality or condition

degrade (v) – To wear by erosion or weathering

degraded (adj) – Reduced in worth or value or worn by erosion or weathering

dehydrate (v) – To lose water or become dry

dehydrated (adj) – 1 : Having lost water and/or become dry  2 : In regards to food, dried to preserve for future use

deity (n) – A god, goddess or other divine entity

delicacy (n) – A choice food

delineate (v) – To draw or trace the outline of

demarcate (v) – To separate clearly as if by boundaries

demilitarized zone (n) – An area between countries in which military forces and installations are forbidden; also called a DMZ

demographics (n) – The statistical breakdown of a population’s characteristics (e.g., age, sex, distribution, density)

denominator (n) – The term below the line in a fraction; the divisor of the numerator

density (n) – The quantity or number per unit (e.g. population density is often measured in number of organisms per square meter unit of area)

deplete (v) – To use up gradually (a resource, strength, etc.)

depleted (adj) – Used up or emptied out

depletion (n) – The gradual using up or destruction of something (e.g., a resource)

deploy (v) – To place or station in a particular locale

depot (n) – A station or stopping place (e.g., for trains, buses, ships)

depression (n) – An area of low barometric pressure, characterized by stormy weather

depth sounder (n) – An instrument that uses sound waves to measure water depth

derivative (adj) – A substance derived from another substance

desalination (n) – The process by which salt is removed from water, especially sea water, to make it drinkable

desalinate (v) – Synonymous to "desalinize"

desalinator (n) – A machine that removes salt from seawater to make fresh water

desalinize (v) – To remove salt from sea water

desolation (n) – Devastation or ruin

detractor (n) – One who speaks disparagingly

detrimental (adj) – Harmful

detritivore (n) – An organism that eats detritus, thus helping to break down organic material within the environment

detritus (n) – Any accumulation of disintegrated material or debris; partially decomposed plant matter that can be used as food

devastating (adj) – Overwhelming, confounding, stunning

developing country (n) – A country that is progressing economically, socially, and politically from an underdeveloped condition

development (n) – A thing that is developed; specifically structures on a tract of land for use by people

deviation (n) – The deflection of a ship’s compass-needle from its magnetic orientation, caused by iron and other potentially magnetized sources on a ship

devout (adj) – Devoted to religion or to the fulfillment of religious obligations; displaying reverence or piety

diameter (n) – The length of a line segment passing through the center of a circle, bisecting it

diaphragm (n) – The partition of muscles and tendons between the abdominal and chest cavities

diatom (n) – Any of a certain class of microscopic algae, one-celled or in colonies, often used as a source of food for other kinds of marine life

dicotyledon (n) – Also called dicot: A flowering plant with two cotyledons (leaves of the embryo of a seed plant) that usually appear at germination

dictator (n) – A ruler with absolute power and authority, especially one who exercises this power and authority tyrannically

dictatorship (n) – A state ruled by a dictator holding absolute power and authority

didgeridoo (n) – A long, traditional wooden trumpet of the Australian aborigines (also spelled didjeridoo)

dinghy (n) – A small boat or rowboat used as a tender to another vessel

dingo (n) – The Australian wild dog (Canis dingo), usually tawny in color, with short, pointed ears and a bushy tail

dinoflagellate (n) – Any of numerous minute, chiefly marine protozoans of the order Dinoflagellata, characteristically having two flagella and often a cellulose shell; some species are bioluminescent and some produce the toxins that cause red tides

dirty fuel (n) – Fuel that is contaminated with water, particles, etc., generally causing an engine to function poorly or not at all

discernible (adj) – Perceptible, visible

discrepancy (n) – Divergence

discriminate (v) – To show prejudice against

disparity (n) – Difference; incongruity

disperse (v) – Scatter in different directions

displacement (n) – The weight or volume of water displaced by a ship

displacement boat (n) – A boat that achieves its buoyancy (ability to float) by displacing a volume of water equal in weight to the boat’s hull and its load

disrupt (v) – To interrupt the normal course of

disruption (n) – An interruption in the normal course of an event

dissipate (v) – To drive away or disperse

distraught (adj) – Troubled, mentally confused, distracted

diurnal (adj) – Active during the day time

divergent evolution (n) – An evolutionary theory that refers to the origin of new populations or species from a common ancestor

diverse (adj) – Varied, different

diversification (n) – 1 : Variety  2 : The process by which a greater variety (of products, industries, species) comes into being

diversify (v) – To make different or diverse; to vary

diversity (n) – The number of different species or types of animals

dividers (n)– An instrument consisting of two pointed legs connected at one end by a pivot, used for taking measurements; also called a "pair of compasses"

docile (adj) – Yielding to supervision, direction, or management; tractable

"dog watch" (n) – Either of the two ship watch periods (from 4–6 p.m. or 6–8 p.m.) which are half the length of a normal watch

doldrums (n) – A part of the ocean near the equator abounding in calms, squalls, and light shifting winds

domain (n) – In mathematics, the set of elements to which a mathematical or logical variable is limited; specifically: the set on which a function is defined

dominant (adj) – In ecological terms, belonging to a species of plant or animal most numerous in a community or exercising control over the other community organisms by its influence on the environment

domino effect (n) – A cumulative effect produced when one event sets off a chain of similar events

dormancy (n) – A state of inactivity or suspended animation

dormant (adj) – Quiet, inactive

dorsal (adj) – On or near the back

dorsal fin (n) – A fin located on the back of a fish or other marine organism

dory (n) – A flat-bottomed, high-sided rowboat, used chiefly in commercial fishing

double-decker bus (n) – A bus that has seats on upper and lower levels

douse (v) – To wrap or roll (as a sail or a flag) close to or around something; to furl a sail

downhaul (n) – A single rope or tackle used to haul down a sail

draft (n) – The depth of water required to float a ship

dragger (n) – A fishing vessel that catches fish by dragging a net along the ocean floor

Dramamine (n) – A medicine used to prevent motion sickness, especially seasickness

draw (n) – The act of taking or pulling out

draw (v) – To need (a specified depth of water) to float in

drawbridge (n) – A bridge that can be raised or drawn to the side to allow for the passage of vessels

dreamtime (n) – In Australian aboriginal lore, the mystical past when spirit gods were believed to inhabit the earth

dredge chain (n) – A chain used to drag the ocean floor for fish, shellfish, etc.

dress (v) – To clean and gut, or eviscerate (e.g. a fish)

dress the yards (v) – A maritime term that refers to sending crew members aloft to stand on the yard footropes as a salute and sign of respect when entering or leaving a port of call

drift (n) – The speed of a water current

drive shaft (n) – A rotating pole that connects the engine to the propeller on a ship

drogue (n) – 1: A float that lies on the surface of the water, heavy enough to be influenced more by water current than the force of the wind; useful in tracking current flow 2: Any object used to increase the drag of a boat and slow her down. Typically shaped like a parachute or cone opened underwater, drogues decrease a boat's speed in heavy weather.

drought (n) – A prolonged period of climatic dryness; it can cause extensive crop damage

drumlin (n) – A long ridge or small, oval-shaped hill, formed by glaciers

dry bag (n) – A waterproof bag in which to keep articles dry while boating

dry skirt (n) – A skirt of waterproof material, worn by kayakers, which fits around the rim of a kayak cockpit to prevent water from entering the kayak even if the boat flips over; often held up by suspenders

drydock (n) – A specialized dock where boats are pulled out of the water to be repaired, painted or inspected; some drydocks allow boats to be floated into a basin, which is then sealed at one end and pumped out

dry suit (n) – A full-length suit, similar in look to a wetsuit but which keeps one entirely dry when worn; often called a "survival suit", a dry suit is most often used by boaters in regions of cold water and stormy weather

dualism (n) – A composition of two parts

dunnage (n) – Lining and packing materials that float

dwindle (v) – To diminish, become less

dynamics (n) – The social, intellectual, or moral forces that produce activity and change in a given sphere

dysentery (n) – A disease characterized by severe diarrhea

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