In linguistics, a tenuis consonant (/ˈtɛn.juːɪs/ ⓘ or /ˈtɛnuːɪs/)[2] is an obstruent that is voiceless, unaspirated and unglottalized.
In other words, it has the "plain" phonation of [p, t, ts, tʃ, k] with a voice onset time close to zero (a zero-VOT consonant), as Spanish p, t, ch, k or English p, t, k after s (spy, sty, sky).
An early IPA convention was to write the tenuis stops ⟨pᵇ, tᵈ, kᶢ⟩ etc.
if the plain letters ⟨p, t, k⟩ were used for aspirated consonants (as they are in English): [ˈpaɪ] 'pie' vs. [ˈspᵇaɪ] 'spy'.
The term tenuis comes from Latin translations of Ancient Greek grammar, which differentiated three series of consonants, voiced β δ γ /b d ɡ/, aspirate φ θ χ /pʰ tʰ kʰ/, and tenuis π τ κ /p˭ t˭ k˭/.