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Webster 1828 Edition

Noun.

A vessel filled with combustibles and furnished with grappling irons to hook and set fire to an enemy's ships.

See also: fire ship

fireship ‎(plural fireships)

(nautical) A sailing ship that has been set alight and left to drift into an opposing fleet. Famously used by Englishman Sir Francis Drake when fighting the Spanish Armada of 1588.
(vulgar, slang) A diseased prostitute.

Depraved and Insulting English – Peter Novobatsky & Ammon Shea ISBN 0-15-601149-2