Evanescence :: Evanescence (n.) The act or state of vanishing away; disappearance; as, the evanescence of vapor, of a dream, of earthly plants or hopes..
Evanescent :: Evanescent (a.) Liable to vanish or pass away like vapor; vanishing; fleeting; as, evanescent joys..
Evanescent :: Evanescent (a.) Vanishing from notice; imperceptible.
Evanescently :: Evanescently (adv. In a vanishing manner) ; imperceptibly.