chivalrous (adj.)

late 14c. (c. 1200 as a surname), "mounted knight, armed horseman of noble birth," from Anglo-French chivaler "mounted knight," Old French chevalier "knight, horseman, knight in chess" (12c., Modern French chevaler), from Late Latin caballarius "horseman" (source of Provençal cavallier, Spanish caballero, Portuguese cavalleiro, Italian cavaliere; see cavalier (n.)). The word was nativized in Middle English ("chevaleer"), but has been given a French pronunciation since 16c.

c. 1300, "body or host of knights; knighthood in the feudal social system; bravery in war, warfare as an art," from Old French chevalerie "knighthood, chivalry, nobility, cavalry, art of war," from chevaler "knight," from Medieval Latin caballarius "horseman," from Latin caballus "nag, pack-horse" (see cavalier).

From late 14c. as "the nobility as one of the estates of the realm," also as the word for an ethical code emphasizing honor, valor, generosity and courtly manners. Modern use for "social and moral code of medieval feudalism" probably is an 18c. historical revival.

1814, from un- (1) "not" + chivalrous. Related: Unchivalrously; unchivalric.