evanescent
Evanescent (adj) means fading away or disappearing quickly.
Etymology
Borrowed from French évanescent (“evanescent”), from Latin ēvānēscēns (“disappearing, vanishing”), the present participle of ēvānēscō (“to disappear, vanish; to die out, fade away; to lapse”). This is formed from ē- (a variant of ex-, prefix meaning ‘away, out’) and vānēscō (“to vanish”) (from vānus (“empty, vacant, void”), from Proto-Indo-European *h₁weh₂- (“to abandon, leave”)), plus -ēscō (suffix forming verbs with the sense ‘to become’).