Interregnum rhymes with:
magnum, aluminium, aluminum, annum, arcanum, barnum, bonum, branam, brannam, brannum, branum, bucknam, burnam, burnham, bynum, canam, debnam, denham, denim, denomme, dornam, downum, dunham, dunnam, duodenum, farnam, farnham, farnum, granum, greenham, hannam, hannum, jeyaretnam, keenum, lanham, lannom, lanthanum, lanum, laudanum, linam, lynam, magnum, menem, mezhdumarodnom, molybdenum, newnam, obshchestvennom, organum, panem, phenom, platinum, plenum, putnam, puttnam, ranum, sonum, steinem, stoneham, swetnam, tottenham, tranum, tympanum, unum, vanname, vanornum, varnum, venom
Interregnum sounds like:
intercession, intercom, intrusion