Source : Webster's Revised Unabridged Dictionary (1913)

Aphonic \A*phon"ic\, Aphonous \Aph"o*nous\, a.
   Without voice; voiceless; nonvocal.

Source : WordNet®

aphonic
     adj : being voiceless through injury or illness and thus incapable
           of all but whispered speech [syn: {voiceless}]