ship of the line

WordReference Random House Unabridged Dictionary of American English © 2025

ship′ of the line′, 

1. Military a former sailing warship armed powerfully enough to serve in the line of battle, usually having cannons ranged along two or more decks;
   battleship.

• 1700–10

Collins Concise English Dictionary © HarperCollins Publishers::

ship of the line noun

1. (formerly) a warship large enough to fight in the first line of battle