The story
Contraction of ship of the line of battle, a warship large enough to be in the line of battle. See also battleship, contracted from the same phrase; and line of battle ship.
Etymology from Wiktionary, CC BY-SA 4.0.
ship of the line
Today it means: 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. Full definition →