sib·i·lant 
(sĭbə-lənt)
(sĭbə-lənt)adj.
Of, characterized by, or producing a hissing sound like that of (s) or (sh): the sibilant consonants; a sibilant bird call.
n.
A sibilant speech sound, such as English (s), (sh), (z), or (zh).
[Latin sībilāns, sībilant-, present participle of sībilāre, to hiss.]
sibi·lance, sibi·lan·cy n.
sibi·lant·ly adv.