volatile adj.

1590s "fine or light," also "evaporating rapidly" (c. 1600), from French volatile, from Latin volatilis "fleeting, transitory; swift, rapid; flying, winged," from past participle stem of volare "to fly" (see volant). Sense of "readily changing, flighty, fickle" is first recorded 1640s. Volatiles in Middle English meant "birds, butterflies, and other winged creatures" (c. 1300).