Ascertain rhymes with:
entertain, pertain, abstain, aquitaine, attain, brattain, buntain, butane, chastain, contain, costain, detain, entertain, fontaine, fountaine, lafountain, lafountaine, lamontagne, maintain, mustain, obtain, partain, pertain, petain, retain, sartain, stain, sustain, uptain
Ascertain sounds like:
accordion, accreditation, accretion, ageratum, agerton, assertion