WordWeb Online

1. Produced without vibration of the vocal cords
   "voiceless consonants such as 'p' and 'k' and 's'";
   - unvoiced, surd, hard
    
2. Deprived of the rights of citizenship especially the right to vote
   "labour was voiceless";
   - disenfranchised, disfranchised, voteless
    
3. Uttered without voice
   "voiceless whispers";
   - breathed
    
4. Being without sound through injury or illness and thus incapable of all but whispered speech
   - aphonic

See also: inarticulate, inaudible, unarticulate, unhearable, whispered

Encyclopedia: Voiceless, the animal protection institute