1580s, "to apportion to someone as his share; to apportion out to others; to enjoy or suffer (something) with others," from share (n.1). Meaning "to divide one's own and give part to others" is recorded from 1590s. Meaning "confess one's sins openly" (1932, implied in sharing) is from "the language of Moral Rearmament" [OED]. Related: Shared; sharer; sharing.