Certainly rhymes with:
uncertainly, uncertainly, clandestinely, uncertainly, wantonly, winstanley, brazenly, clandestinely, commonly, evenly, gentlemanly, genuinely, heavenly, humanly, matronly, mistakenly, openly, slovenly, spokenly, suddenly, uncertainly, uncommonly, unevenly, wantonly, winstanley
Certainly sounds like:
cardinal, cardinale, cardinali, cartmell, cartmill, crouthamel