clan·nish \ˈklanish, -aan-, -nēsh\adjective 1.archaic: of or relating to a clan < clannish ceremonies > 2.: characteristic or suggestive of clan psychology or organization < clannish loyalty > specifically: tending to associate only with others of like origins, sympathies, and prejudices < clannish immigrants > < clannish party members > • clan·nish·nessnoun-es