Maritime terms are not a row of isolated definitions.

Advancing the last reliable position by each course, speed and elapsed time while uncertainty from current and instruments accumulates.

A unit of speed equal to one nautical mile per hour, or 1.852 kilometres per hour—not a unit of distance.

The distance unit used in marine navigation, defined internationally as exactly 1,852 metres.

A traditional British and American depth unit of six feet, or 1.8288 metres; old charts still require their own legends.

A graduated line and lead weight used to read depth at bottom contact and, with an armed base, sample seabed material.

The vertical reference to which charted depths are reduced so observations made at different water levels can be compared.

A magnetized direction instrument whose card supplies heading; it does not determine position by itself.

A double-reflection instrument that brings a celestial image to the horizon and measures the angle for celestial navigation.

A precise shipboard timekeeper preserving reference-meridian time so comparison with local astronomical time can yield longitude.

The wind experienced aboard, formed by the vector combination of true wind and the airflow caused by the vessel's motion.

Downwind displacement caused by transverse wind force; underwater lateral resistance reduces but does not eliminate it.

Turning the bow through the wind so the sails fill on the opposite side; repeated tacks create progress to windward.

A sail carried from an athwartship yard; its name describes the setting, not a requirement for a geometrically square outline.

A sail working chiefly along the vessel's length, readily trimmed to apparent wind and generally effective to windward.

A rig of at least three masts, square-rigged forward and fore-and-aft rigged on the aftermost mast.

The principal fore-and-aft structure along the bottom of a hull, carrying loads and often contributing underwater lateral resistance.

Weight carried to manage stability, draft and trim; historical forms included stone, sand, brick and iron kentledge.

The vertical distance from the waterline to the lowest immersed part of a vessel, changing with loading and water density.

The fore-and-aft attitude expressed through the difference between forward and after draft, altered by weight distribution.

The horizontal separation GZ between the vertical lines of weight and buoyancy when a vessel heels; displacement times GZ is righting moment.

A person, and often the privately financed vessel, commissioned by a state in a particular war to capture specified enemy shipping.

A wartime state commission for a private armed vessel, limited by the issuing system's enemies, duration and procedure.

A court deciding whether a maritime capture was lawful prize and adjudicating ownership, neutral claims and disposition.

Maritime violence or depredation without authority recognized by the applicable law; precise definitions vary across period and jurisdiction.