Costain rhymes with:
abstain, chastain, mustain, stain, sustain, abstain, aquitaine, ascertain, attain, brattain, buntain, butane, chastain, contain, detain, entertain, fontaine, fountaine, lafountain, lafountaine, lamontagne, maintain, mustain, obtain, partain, pertain, petain, retain, sartain, stain, sustain, uptain
Costain sounds like:
cadam, cadden, cadena, cadman, cadmium, caetano, castano, castanon, casteen, casten, castine, caston, catain, catania, catano, catena, catino, caton, catone, cattaneo, cattani, catton, catwoman, causation, cauthen, cauthon, caution, cawthon, caxton, cayton, cedeno, cessation, chadian, chastain, chasteen, chasten, chatham, chatman, chatmon, chattin, chatwin, chaudoin, cheatham, cheatum, cheetan, cheetham, chestman, cheston, chetwin, chittum, chutney, citation, cittadino, coatney, cogitation, cookston, costano, costen, costin, coston, costume, cotham, cotman, cotney, cottam, cotten, cottman, cottom, cotton, cottone, cowden, cudney, custodian, custom, cuttino, cydonia, cyhexatin