means The brother of your mother or father, or the husband of your aunt — a member of the generation above you who isn't a parent.

from From Old French 'oncle,' which descends from Latin 'avunculus,' literally 'little grandfather' or 'mother's brother' — a tender diminutive of 'avus,' grandfather. The maternal-uncle flavor lingers in English 'avuncular,' meaning kindly in an uncle-ish way. Latin 'avunculus' is also the root of 'avuncular' patterns across Europe, and the cry 'say uncle!' (meaning 'give up') is a much later American slang twist of unclear origin, possibly echoing an older appeal to an elder for mercy.