Etymology

Contraction of line of battle ship, a warship large enough to be in the line of battle.

Noun

ship of the line

1. a large square-rigged warship large enough to have a place in the line of battle. with up to 140 guns on at least two decks. A capital ship from the age of sail, superior to a frigate; usually, a seventy-four, or three-decker. (Totten).

The OED records the terms line of battle ship, battleship, ship of the line and liner being used interchangeably up through the 19th century. In modern usage ship of the line is a wooden line of battle ship from the age of sail; battleship is an armoured and motorized warship of the late 19th and mid 20th centuries.

Synonyms

• (square-rigged warship): man-of-war
• (vessel superior to frigate): line of battle ship; liner

See also

• Wikipedia article on Ship of the Line (a square-rigged warship)