Source : Webster's Revised Unabridged Dictionary (1913)

Siss \Siss\, v. i. [Of imitative origin; cf. D. sissen, G.
   zischen.]
   To make a hissing sound; as, a flatiron hot enough to siss
   when touched with a wet finger. [Colloq. U. S.; Local, Eng.]

Siss \Siss\, n.
   A hissing noise. [Colloq. U. S.]

Source : WordNet®

siss
     v 1: express or utter with a hiss [syn: {hiss}, {sizz}, {sibilate}]
     2: make a sharp hissing sound, as if to show disapproval [syn:
        {hiss}, {sizz}, {sibilate}]