by ear
Tom toca piano de ouvido.
Tom plays the piano by ear.
Tom está com dor de ouvido.
Tom has an earache.
I have an earache.
Ele sabia tocar violão de ouvido, sem partitura.
He knew how to play the guitar by ear, without sheet music.
Eu estou com uma infecção de ouvido.
I have an ear infection.
She plays the piano by ear.
Uma testemunha ocular vale mais que dez testemunhas de ouvido.
An eyewitness is worth ten people who only heard about it.