adventure:  Adventure derives ultimately from a Latin verb meaning ‘arrive’. It originally meant ‘what comes or happens by chance’, hence ‘luck’, but it took a rather pessimistic downturn via ‘risk, danger’ to (in the 14th century) ‘hazardous undertaking’. Its Latin source was advenīre, formed from the prefix adand venīre ‘come’. Its past participle stem, advent-, produced English advent  and adventitious , but it was its future participle, adventura ‘about to arrive’, which produced adventure.
In the Romance languages in which it subsequently developed (Italian avventura, Spanish aventura, and French aventure, the source of Middle English aventure) the d disappeared, but it was revived in 15th – 16thcentury French in imitation of Latin. The reduced form venture first appears in the 15th century. => adventitious, avent, venture
c. 1200, 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 adventurus, future participle of advenire "to come to, reach, arrive at," from ad- "to" (see ad-) + venire "to come" (see venue).
Meaning developed through "risk/danger" (a trial of one's chances), c. 1300, and "perilous undertaking" (late 14c.) and thence to "a novel or exciting incident" (1560s). Earlier it also meant "a wonder, a miracle; accounts of marvelous things" (13c.). The -d- was restored 15c.-16c. Venture is a 15c. variant.