early 15c., "inclined to fighting," from Latin bellicosus "warlike, valorous, given to fighting," from bellicus "of war," from bellum "war" (Old Latin duellum, dvellum), which is of uncertain origin.

The best etymology for duellum so far has been proposed by Pinault 1987, who posits a dim. *duelno- to bonus. If *duelno- meant 'quite good, quite brave', its use in the context of war (bella acta, bella gesta) could be understood as a euphemism, ultimately yielding a meaning 'action of valour, war' for the noun bellum. [de Vaan]

"be victorious," c. 1300 fusion of Old English winnan "to labor, toil, struggle for, work at, strive, fight," and gewinnan "to gain or succeed by struggling, conquer, obtain," both from Proto-Germanic *wennanan "to seek to gain" (source also of Old Saxon winnan, Old Norse vinna, Old Frisian winna, Dutch winnen "to gain, win," Danish vinde "to win," Old High German winnan "to strive, struggle, fight," German gewinnen "to gain, win," Gothic gawinnen "to suffer, toil"), from PIE root *wen- (1) "to desire, strive for."

Related: Won; winning. Meaning "gain the affection or esteem of" is from c. 1600. Breadwinner preserves the sense of "toil" in Old English winnan. Phrase you can't win them all (1954) first attested in Raymond Chandler. Winningest is attested by 1804.

war games played on maps with blocks representing bodies of soldiers, 1873 (once, from 1811, as a German word in English), from German Kriegsspiel, literally "war game," from Krieg "war," from Middle High German kriec, "combat," mostly "exertion, effort; opposition, enmity, resistance," from Old High German chreg "stubbornness, defiance, obstinacy," from Proto-Germanic *krig-, which is perhaps from PIE root *gwere- (1) "heavy" or cognate with Greek hybris "violence" (see hubris; also see war (n.)). For second element, see spiel (n.). Introduced 1870s as officer training in British army.

also antiwar, "opposition to a war," 1812, American English, in reference to opposition to the War of 1812, from anti- + war (n.). In a non-specific sense of "political pacifism, opposition to all war," by 1821.

U.S. state, river, and native tribe, all named for the bay, which was named for Baron (commonly "Lord") De la Warr (Thomas West, 1577-1618), first English colonial governor of Virginia. The family name is attested from 1201, from Delaware in Brasted, Kent, which is probably ultimately from de la werre "of the war" (a warrior), from Old French werre/guerre "war" (see war (n.)).  Related: Delawarean.

"fighter in an irregular, independent armed force," 1809, from Spanish guerrilla "body of skirmishers, skirmishing warfare," literally "little war," diminutive of guerra "war," from a Germanic source cognate with Old High German werra "strife, conflict, war," from Proto-Germanic *werra- (see war (n.)). Acquired by English during the Peninsular War (1808-1814), when bands of Spanish peasants and shepherds annoyed the occupying French. Purists failed in their attempt to keep this word restricted to "irregular warfare" and prevent it taking on the sense properly belonging to guerrillero "guerrilla fighter." Figurative use by 1861. As an adjective from 1811.

1939, in reference to the period between the world wars, from inter- + war (n.).

late 14c., "a soldier;" see man (n.) + war (n.). Meaning "armed ship, vessel equipped for warfare" is from late 15c. Man in the sense of "a ship" is attested from late 15c. in combinations (such as merchantman). The sea creature known as the Portuguese man-of-war (1707) is so called for its sail-like crest. The great U.S. thoroughbred race horse was Man o' War (1917-1947).

also post-war, "being or occurring after a (particular) war," 1906, in reference to the U.S. Civil War, a hybrid from post- + war (n.). Compare post-bellum.

"military science," c. 1400, from war (n.) + craft (n.).