Propper rhymes with:
improper, proper, cropper, dropper, gropper, improper, proper, bopper, chopper, clopper, copper, cropper, dropper, gropper, hopper, improper, kopper, opper, popper, proper, shopper, stopper, topor, topper, whopper
Propper sounds like:
periphery, porphyry, prefer, prepare, preparer, proffer, proper, provera, purifier, purveyor