WordWeb Online

1. Produced without vibration of the vocal cords
   "unvoiced consonants such as 'p' and 'k' and 's'";
   - voiceless, surd, hard
    
2. Not made explicit
   "the unvoiced terms of the agreement";
   - unexpressed, unsaid, unstated, unuttered, unverbalized, unverbalised [Brit], unspoken

See also: implicit, inexplicit, whispered

Antonym: soft

Encyclopedia: Unvoiced