evanescence

from WordNet (r) 3.0 (2006)

evanescence
    n 1: the event of fading and gradually vanishing from sight;
         "the evanescence of the morning mist"

from The Collaborative International Dictionary of English v.0.48

Evanescence \Ev`a*nes"cence\, n.
   The act or state of vanishing away; disappearance; as, the
   evanescence of vapor, of a dream, of earthly plans or hopes.
   --Rambler.
   [1913 Webster]