What is the meaning of Tenuis?

Of Greek consonants, neither aspirated nor voiced, as [p], [t], [k]

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.).

A tenuis consonant.

thin, slender, slim, lank; especially:

synonym of mānēs, the manes

fine, rare, thin; pure, clear, not coarse

weak, feeble, tenuous

little, slight, trifling

delicate, subtle

Source: wiktionary.org