Mammoth Uncensored Word List:
31 words ending with sm, 16 letters long

accommodationism anthropocentrism anthropomorphism antievolutionism antireductionism authoritarianism collaborationism communitarianism configurationism consequentialism controversialism countercriticism counterterrorism electromagnetism environmentalism epiphenomenalism gynandromorphism hypercortisolism hyperpituitarism institutionalism internationalism introspectionism multiculturalism necessitarianism premillennialism pseudoclassicism psychopannychism superromanticism supranationalism transnationalism ultranationalism