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1. Pronounce with an initial sibilant
    
2. Utter a sibilant
    
3. Express or utter with a hiss
   - hiss, sizz, siss
    
4. Make a sharp hissing sound, as if to show disapproval
   - hiss, siss, sizz

Derived forms: sibilating, sibilates, sibilated

Type of: articulate, emit, enounce, enunciate, let loose, let out, mouth, pronounce, say, sound out, speak, talk, utter, verbalise [Brit], verbalize