Threefold rhymes with:
billfold, blindfold, centerfold, eightfold, fivefold, manifold, ninefold, penfold, saffold, sevenfold, sixfold, tenfold
Threefold sounds like:
thorvald, travelday, traveled, travelled, travolta, trebled, tripled, triplet, triplett, triviality, troubled, trueblood