Of short duration. [L. e, out, + vanesco, to vanish]
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ev·a·nes·cent .ev-ə-'nes-ənt adj tending to disappear quickly: of relatively short duration <an \evanescent rash>
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ev·a·nes·cent (ev″ə-nesґənt) [L. evanescere to vanish away] vanishing; passing away quickly; unstable; unfixed.Medical dictionary. 2011.