adjective: (linguistics) Of Greek consonants, neither aspirated nor voiced, as [p], [t], [k]
adjective: (linguistics) Of obstruents in other languages, not voiced, aspirated, glottalized, or otherwise different in phonation from the prototypical values of the voiceless IPA letters ([p], [t], [k], [f], [θ], [s], [ʃ], etc.).
