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).
late Old English wyrre, werre "large-scale military conflict," from Old North French werre "war" (Old French guerre "difficulty, dispute; hostility; fight, combat, war;" Modern French guerre), from Frankish *werra, from Proto-Germanic *werz-a- (source also of Old Saxon werran, Old High German werran, German verwirren "to confuse, perplex"), from PIE *wers- (1) "to confuse, mix up". Cognates suggest the original sense was "to bring into confusion."
Spanish, Portuguese, and Italian guerra also are from Germanic; Romanic peoples turned to Germanic for a "war" word possibly to avoid Latin bellum (see bellicose) because its form tended to merge with bello- "beautiful." There was no common Germanic word for "war" at the dawn of historical times. Old English had many poetic words for "war" (wig, guð, heaðo, hild, all common in personal names), but the usual one to translate Latin bellum was gewin "struggle, strife" (related to win (v.)).
First record of war-time is late 14c. Warpath (1775) originally is in reference to North American Indians, as are war-whoop (1761), war-paint (1826), and war-dance (1757). War crime is attested from 1906 (in Oppenheim's "International Law"). War chest is attested from 1901; now usually figurative. War games translates German Kriegspiel (see kriegspiel).
The causes of war are always falsely represented ; its honour is dishonest and its glory meretricious, but the challenge to spiritual endurance, the intense sharpening of all the senses, the vitalising consciousness of common peril for a common end, remain to allure those boys and girls who have just reached the age when love and friendship and adventure call more persistently than at any later time. The glamour may be the mere delirium of fever, which as soon as war is over dies out and shows itself for the will-o'-the-wisp that it is, but while it lasts no emotion known to man seems as yet to have quite the compelling power of this enlarged vitality. [Vera Brittain, "Testament of Youth"]
The world will never have lasting peace so long as men reserve for war the finest human qualities. [John Foster Dulles, Speech on the Marshall Plan, 1948]
"a featherless plantigrade biped mammal of the genus Homo" [Century Dictionary], Old English man, mann "human being, person (male or female); brave man, hero;" also "servant, vassal, adult male considered as under the control of another person," from Proto-Germanic *mann- (source also of Old Saxon, Swedish, Dutch, Old High German man, Old Frisian mon, German Mann, Old Norse maðr, Danish mand, Gothic manna "man"), from PIE root *man- (1) "man." For the plural, see men.
Sometimes connected to root *men- (1) "to think," which would make the ground sense of man "one who has intelligence," but not all linguists accept this. Liberman, for instance, writes, "Most probably man 'human being' is a secularized divine name" from Mannus [Tacitus, "Germania," chap. 2], "believed to be the progenitor of the human race."
Specific sense of "adult male of the human race" (distinguished from a woman or boy) is by late Old English (c. 1000); Old English used wer and wif to distinguish the sexes, but wer began to disappear late 13c. and was replaced by man. Universal sense of the word remains in mankind and manslaughter. Similarly, Latin had homo "human being" and vir "adult male human being," but they merged in Vulgar Latin, with homo extended to both senses. A like evolution took place in Slavic languages, and in some of them the word has narrowed to mean "husband." PIE had two other "man" roots: *uiHro "freeman" (source of Sanskrit vira-, Lithuanian vyras, Latin vir, Old Irish fer, Gothic wair; see *wi-ro-) and *hner "man," a title more of honor than *uiHro (source of Sanskrit nar-, Armenian ayr, Welsh ner, Greek anēr; see *ner- (2)).
Man also was in Old English as an indefinite pronoun, "one, people, they." It was used generically for "the human race, mankind" by c. 1200. As a word of familiar address, originally often implying impatience, c.1400; hence probably its use as an interjection of surprise or emphasis, since Middle English but especially popular from early 20c.
As "a woman's lover," by mid-14c. As "adult male possessing manly qualities in an eminent degree," from 14c. Man's man, one whose qualities are appreciated by other men, is by 1873. Colloquial use of the Man for "the boss" is by 1918. To be man or mouse "be brave or be timid" is from 1540s. Meaning "piece with which a game (especially chess) is played" is from c. 1400.
Man-about-town "man of the leisure class who frequents clubs, theaters, and other social resorts" is from 1734. Man of the world is from mid-14c. as "secular man, layman;" by early 15c. as "man experienced in the ways of the world, one able to take things in stride." To do something as one man "unanimously" is from late 14c.
So I am as he that seythe, 'Come hyddr John, my man.' 
MANTRAP, a woman's commodity. [Grose, "Dictionary of the Vulgar Tongue," London, 1785]
At the kinges court, my brother, Ech man for himself. [Chaucer, "Knight's Tale," c. 1386]
1610s, the language of Portugal, also (1620s) a resident of Portugal; 1660s as an adjective, "of or pertaining to Portugal," from Portuguese Portuguez (see Portugal + -ese). The ending was vulgarly mistaken for a plural in English, and false singular Portugee (by 1821) was formed. Compare Chinee from Chinese; also portegue, portague (1530s), name of a gold coin from Portugal, apparently also a false singular. For Portuguese man-of-war, see man-of-war.
Middle English mannen, from Old English mannian "to furnish (a fort, ship, etc.) with a company of men," from man (n.). Meaning "to take up a designated position on a ship" is first recorded 1690s. Meaning "behave like a man, brace up in a manful way, act with courage" is from c. 1400. To man (something) out "play a man's part, bear oneself stoutly and boldly" is from 1660s. Related: Manned; manning.