Unionism rhymes with:
communism, abolitionism, agrarianism, americanism, anachronism, antagonism, arianism, authoritarianism, buchananism, chauvinism, communism, confucianism, creationism, determinism, egalitarianism, expansionism, expressionism, hedonism, hellenism, hooliganism, humanism, illusionism, impressionism, interventionism, isolationism, mechanism, microorganism, obstructionism, organism, paganism, perfectionism, peronism, protectionism, puritanism, reaganism, republicanism, revisionism, satanism, sectarianism, tokenism, totalitarianism, zionism
Unionism sounds like:
uncanny, uncommon, unicom, unikom, unisom, unison, unknown, unosom, unscom, unseen, unshaken