Source : Webster's Revised Unabridged Dictionary (1913)

Voiceless \Voice"less\, a.
   1. Having no voice, utterance, or vote; silent; mute; dumb.

            I live and die unheard, With a most voiceless
            thought, sheathing it as a sword.     --Byron.

   2. (Phon.) Not sounded with voice; as, a voiceless consonant;
      surd.

   {Voiceless stop} (Phon.), a consonant made with no audible
      sound except in the transition to or from another sound; a
      surd mute, as p, t, k. -- {Voice"less*ly}, adv. --
      {Voice"less*ness}, n.

Source : WordNet®

voiceless
     adj 1: of speech sounds [syn: {surd}, {unvoiced}] [ant: {sonant}]
     2: not using the voice; "unvoiced thoughts"; "unvoiced
        consonants such as `p' and `k' and `s'" [syn: {unvoiced}]
        [ant: {voiced}]
     3: uttered without voice; "could hardly hear her breathed plea,
        `Help me'"; "voiceless whispers" [syn: {breathed}]
     4: being voiceless through injury or illness and thus incapable
        of all but whispered speech [syn: {aphonic}]