1911 Encyclopædia Britannica/Uncle

UNCLE, the brother of a person's father or mother, also the husband of one's aunt (i.e. the sister of a father or mother). The French oncle, which appears in Anglo-French as uncle, comes from a Late Latin unculus, a shortened form of the Latin avanculus, a maternal uncle, the brother of one's mother. The word is a diminutive of avus, grandfather. The Latin for a paternal uncle is patruus. “Aunt” comes through the Old French aunte, ante, corrupted into the modern tante, from Latin amita, a father's sister, a paternal aunt, the maternal aunt being called matertera.