ship of the line

Short definition from Wiktionary

Noun

1. 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.
2. 2
   Alternative spelling of ship of the line.