Fasten rhymes with:
fason, assassin, bason, cason, casson, chason, clason, classen, classon, fason, gassen, glasson, hassen, hasson, kassan, kassen, kasson, klassen, lassen, masson, mcglasson, nason, passon, sasson, stassen
Fasten sounds like:
facedown, faction, faustian, faustina, faustine, faustino, festoon, fiction, fightin', fixation, fochtman, fuston