The uniauris. Well, if we can have a mythical creature called a unicorn, based on Latin root-words meaning 'one horn', I can see no reason why we shouldn't have another one called a uniauris, based on Latin root-words meaning 'one ear'!
I am really stretching it here... Birds have their inner ears connected so as to instantly calculate the minute difference in time of receiving sounds from each orifice, enabling them to accurately perceive which direction the sound is coming from. I suppose you could call this one ear as the whole caboodle works as one, unlike mammal ears which work independently.