Synonyms for Cinch (same or very similar meaning)
WordNet sense 1 (stable gear consisting of a band around a horse's belly that holds the saddle in place):
girthWordNet sense 2 (any undertaking that is easy to do):
breeze, picnic, pushover, snap, walkover, duck soup, piece of cake, child's playFrom the ODE community, based on WordNetadd/edit