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]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "sibilation":
   aphonia, artificial voice, broken speech, broken tones,
   broken voice, childish treble, choked voice, cracked voice, croak,
   crow, dysarthria, dyslalia, dyslogia, dysphasia, dysphonia,
   dysphrasia, falsetto, harshness, hawking voice, hiss, hoarseness,
   idioglossia, idiolalia, impairment of speech, lisp, lisping,
   loss of voice, muzzy speech, nasal tone, nasalization, quaver,
   shake, speech defect, speech impediment, tremor, twang