translucency

from WordNet (r) 3.0 (2006)

translucency
    n 1: the quality of allowing light to pass diffusely [syn:
         {translucence}, {translucency}, {semitransparency}]

from The Collaborative International Dictionary of English v.0.48

Translucence \Trans*lu"cence\, Translucency \Trans*lu"cen*cy\,
   n.
   The quality or state of being translucent; clearness; partial
   transparency. --Sir T. Browne.
   [1913 Webster]
   [1913 Webster]