Fortnight rhymes with:
whitenight, ammonite, basnight, bauknight, bentonite, canaanite, clintonite, finite, franklinite, goodnight, hignight, hignite, lignite, limonite, maronite, masonite, mennonite, midnight, monzonite, newsnight, reaganite, samsonite, selenite, suburbanite, unite, urbanite, whitenight