Source : Webster's Revised Unabridged Dictionary (1913)

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

         He, with a long, low sibilation, stared. --Tennyson.

Source : WordNet®

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}]
     2: pronunciation with a sibilant (hissing or whistling) sound
        [syn: {assibilation}]