evanescent

"The similarity between the evanescent greetings of the Duchesse de Lambresac and those of my grandmother's friends had begun to arouse my interest by showing me how in all narrow and closed societies, be they those of the minor gentry or of the great nobility, the old manners persist, enabling us to recapture, like an archaeologist, something of the upbringing, and the ethos it reflects, that prevailed in the days of the Vicomte d'Arlincourt and Loiisa Puget."
--Sodom and Gomorrah by Marcel Proust, translated by C.K. Scott Moncrieff and Terence Kilmartin, revised by D.J. Enright, p 110 of the Modern Library paperback edition

"Adrift in a new world of often devastating change, they found meaning in the shifting light on a river at dawn, or the evanescent flash of a hummingbird's flight."
- A Summer of Hummingbirds by Christopher Benfey, p 4

ev-uh-nes-uhnt ~adjective 1. vanishing; fading away; fleeting.
2. tending to become imperceptible; scarcely perceptible.

This seems to be Latin in contrast to the Greek ephemeral.