Battleship

google

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late 18th century: shortening of line-of-battle ship, originally with reference to the largest wooden warships.

wiktionary

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battle +‎  ship; shortened from  line-of- battle ship, attested 1794. 

etymonline

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battleship (n.)

also battle-ship, "powerful warship designed to fight in a line of battle," 1794, shortened from line-of-battle ship (1705), one large enough to take part in a main attack (formerly one of 74-plus guns); from battle (n.) + ship (n.). Later in U.S. Navy it was used of a class of ships that carried guns of the largest size. Rendered obsolete by seaborne air power and guided missiles, the last was decommissioned in 2006. Battleship-gray as a color is attested from 1916. Fighter and bomber airplanes in World War I newspaper articles sometimes were called battleplanes, but it did not catch on.