The Collaborative International Dictionary of English v.0.48:

Sibilation \Sib`i*la"tion\, n. [L. sibilatio.]
   Utterance with a hissing sound; also, the sound itself; a
   hiss.
   [1913 Webster]

         He, with a long, low sibilation, stared. --Tennyson.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sibilation
    n 1: a fricative sound (especially as an expression of
         disapproval); "the performers could not be heard over the
         hissing of the audience" [syn: hiss, hissing,
         hushing, fizzle, sibilation]
    2: pronunciation with a sibilant (hissing or whistling) sound
       [syn: sibilation, assibilation]