Definition of men-of-war:
(n) :
(military, nautical, chiefly historical) A powerful armed naval vessel, primarily one armed with cannon and propelled by sails; a warship.
(n) :
(military, archaic except humorous) A man whose occupation is fighting in wars; a soldier, a warrior.
(n) :
(specifically, US) The Arctic skua (Stercorarius parasiticus).
(n) :
(specifically, archaic) A frigatebird (family Fregatidae), especially the magnificent frigatebird (Fregata magnificens).
(n) :
(obsolete, rare) In full man-of-war's-man: a sailor serving on board an armed naval vessel.
(n) :
Ellipsis of Portuguese man-of-war (“Physalia physalis, a jellyfish-like marine cnidarian consisting of a floating colony of hydrozoans attached to a float”). [Physalia physalis, a marine cnidarian consisting of a floating colony of hydrozoans attached to a float, superficially resembling a jellyfish.]