Retardant rhymes with:
ardent, ardent, discordant, mordant, abundant, accident, antecedent, antioxidant, ardent, ascendant, attendant, coincident, confident, corespondent, correspondent, couldn't, decadent, decedent, defendant, dependent, descendant, descendent, despondent, didn't, discordant, evident, hadn't, imprudent, incident, independent, interdependent, mordant, needn't, nonresident, overconfident, overdependent, oxidant, pendant, precedent, provident, prudent, radant, redundant, resident, resplendent, respondent, rodent, self-confident, shouldn't, strident, student, superintendant, superintendent, transcendent, trident, verdant, vice-president, wouldn't