"companionship, fellowship, association with others," c.1600, from Middle French sodalité or directly from Latin sodalitatem (nominative sodalitas) "companionship, a brotherhood, association, fellowship," from sodalis "companion," perhaps literally "one's own, relative," related to suescere "to accustom," from PIE *swedh-, extended form of root *s(w)e-, pronoun of the third person and reflexive (see idiom). Especially of religious guilds in the Catholic Church.