1555, "one who takes part with another, zealous supporter," from M.Fr. partisan (15c.), from dial. upper It. partezan (Tuscan partigiano) "member of a faction, partner," from parte "part, party," from L. partem (nom. pars), see part (n.). Sense of "guerilla fighter" is first recorded 1692. The adj. is 1708 for warfare, 1842 for politics.