sibilate

sibilate (http://definr.com/sibilate)

     v 1: pronounce with an initial sibilant
     2: utter a sibilant
     3: express or utter with a hiss [syn: hiss, sizz, siss]
     4: make a sharp hissing sound, as if to show disapproval [syn:
        hiss, siss, sizz]