Flatten rhymes with:
flaten, flaten, latin, laton, platen, platten, slaton, slatten, slatton, batten, batton, bratten, bratton, caton, catton, craton, fatten, flaten, gatten, gatton, grattan, gratton, hattan, hatten, hatton, latin, laton, manhattan, matton, mchatton, patane, paton, patten, patton, platen, platten, satin, slaton, slatten, slatton, staten, staton, statton, stratton, vanpatten
Flatten sounds like:
feldene, feldman, feldmann, felten, feltman, felton, fielden, flaten, flodin, flotation, flowton, folden, foliation, foltene, fulltime, fulton