Constant's rhymes with:
constants, constants, constants, assistants, constants, contestants, decongestants, protestants, accountant's, accountants, accountants', assistants, combatants, constants, consultant's, consultants, contestants, decongestants, disinfectants, incompetents, inhabitants, irritants, militants, mutants, noncombatants, patents, pollutants, protestants
Constant's sounds like:
concatenates, constants, constituents, constituents'