The Collaborative International Dictionary of English v.0.48:

Susurration \Su`sur*ra"tion\, n. [L. susurratio, fr. susurrare
   to whisper: cf. F. susurration.]
   A whispering; a soft murmur. "Soft susurrations of the
   trees." --Howell.
   [1913 Webster]

WordNet (r) 3.0 (2006):

susurration
    n 1: the indistinct sound of people whispering; "a soft susurrus
         of conversation" [syn: susurration, susurrus]
    2: speaking softly without vibration of the vocal cords [syn:
       whisper, whispering, susurration, voicelessness]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "susurration":
   aspiration, bated breath, breath, breathy voice, drone, droning,
   exhalation, gabble, gibber, gibbering, jabber, jibber,
   little voice, low voice, maundering, mouthing, mumble, mumbling,
   murmur, murmuration, murmuring, mutter, muttering, rumor, sigh,
   soft voice, stage whisper, still small voice, susurrus,
   underbreath, undertone, whisper, whispering