quies

Quies, quietis is third declension feminine. The stem is quiet-, so every case after the nominative shows the t: quietem, quietis, quiete. From it come quietus, "calm", quiesco, "I come to rest", and requies, "repose", which is the word in requiescat in pace.

Note that quies is not simply the absence of noise. It is the condition of having stopped: rest from work, peace after war, sleep at night, and in funerary inscriptions death itself. The ablative quiete doubles as the adverb "quietly", which is where English quiet, quit, acquit and requiem all begin. Do not confuse the nominative quies with quies as a form of queo, "I am able", which is rare but real.