evanescence (n.)youdaoicibaDictYouDict
1751, "process of gradually vanishing;" see evanescent + -ence. Meaning "quality of being evanescent" is from 1830. Evanescency is attested from 1660s.
evanescent (adj.)youdaoicibaDictYouDict
1717, "on the point of becoming imperceptible," from French évanescent, from Latin evanescentem (nominative evanescens), present participle of evanescere "disappear, vanish, pass away," figuratively "be forgotten, be wasted," from assimilated form of ex- "out" (see ex-) + vanescere "vanish" (see vanish). Sense of "quickly vanishing, having no permanence" is by 1738.
vanish (v.)youdaoicibaDictYouDict
"disappear quickly," c. 1300, from shortened form of esvaniss-, stem of Old French esvanir "disappear; cause to disappear," from Vulgar Latin *exvanire, from Latin evanescere "disappear, pass away, die out," from ex- "out" (see ex-) + vanescere "vanish," inchoative verb from vanus "empty" (see vain). Related: Vanished; vanishing; vanishingly. Vanishing point in perspective drawing is recorded from 1797.