Here's what rhymes with costiveness.
exhaustiveness Words that almost rhyme with costiveness
waspishness heartedness carsickness goriness haughtiness soreness naughtiness balminess heartsickness cognisance morbidness suaveness bigheartedness responsiveness oxidants kindheartedness downheartedness inconspicuous garnishments hardheartedness recognisance subcontinents warmheartedness unresponsiveness overconfidence exorbitance tenderheartedness accomplishments acknowledgments acknowledgements intoxicants admonishments