c. 1200, aventure, auenture "that which happens by chance, fortune, luck," from Old French aventure (11c.) "chance, accident, occurrence, event, happening," from Latin adventura (res) "(a thing) about to happen," from fem. of adventurus, future participle of advenire "to come to, reach, arrive at," from ad "to" (see ad-) + venire "to come," from a suffixed form of PIE root *gwa- "to go, come."
Meaning developed through "risk; danger" (a trial of one's chances), c. 1300, and "perilous undertaking" (late 14c.) to "novel or exciting incident, remarkable occurrence in one's life" (1560s). Earlier it also meant "a wonder, a miracle; accounts of marvelous things" (13c.). The -d- was restored in English 15c.-16c.; attempt was made about the same time to restore it in French, but there it was rejected. Venture is a 15c. variant. German Abenteuer is a borrowing of the French word, apparently deformed by influence of Abend "evening."
c. 1300, aventuren, "to risk the loss of," from Old French aventurer (12c.) "wander, travel; seek adventure; happen by chance," from aventure (n.); see adventure (n.). Meaning "take a chance" is early 14c. Related: Adventured; adventuring.