Synonyms for Unvoiced (same or very similar meaning)
WordNet sense 1 (produced without vibration of the vocal cords):
hard, voiceless, surdWordNet sense 2 (not made explicit):
unexpressed, unsaid, unspoken, unstated, unuttered, unverbalised, unverbalizedWordNet sense 3 (implied though not directly expressed; inherent in the nature of something):
implicit, inexplicitFrom the ODE community, based on WordNetadd/edit