auris

Auris, auris, f., is third declension and an i-stem, so the genitive plural is aurium. The idioms are the useful part: aures dare or praebere alicui, "give somebody a hearing", and aure captus, "deaf", literally "caught by the ear" - the same construction as oculis captus for blind, where the ablative names what has been taken away.

Its verb is audio, and auscultare, "listen hard, obey", is from the same root. The look-alikes are a nuisance and worth naming: aurum is gold and aureus is golden, from an entirely different root, and aura is a breeze. Auris, aurum, aura - one letter apart, three unrelated meanings, all common.