the word 'uncle' entered english in the 13th century from the old french 'oncle', which itself descended from the latin 'avunculus', a diminutive of 'avus' meaning "grandfather." specifically, 'avunculus' referred to a mother's brother, a distinction that was lost in its journey into english, where it generalized to mean any parental sibling or their spouse. this semantic broadening is a common feature of kinship terms as they are adopted into new languages, simplifying specific ancestral distinctions for everyday use.

the word is a simplex borrowing from old french, ultimately from latin 'avunculus', meaning "maternal uncle." it does not contain separable morphemes in modern english spelling.