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1717, from French évanescent, from Latin evanescentem (nominative evanescens), present participle of evanescere "disappear, vanish," from ex- "out" (see ex-) + vanescere "vanish" (see vanish).
evanescent ev·a·nes·cent (ěv'ə-něs'ənt)adj. Of short duration; passing away quickly.