Oughtn't rhymes with:
accountant, adjutant, assistant, blatant, combatant, concomitant, consistent, constant, consultant, contant, contestant, decongestant, disinfectant, distant, existent, exorbitant, expectant, extant, exultant, halperstant, hesitant, important, impotent, inadvertent, incompetent, inconsistent, inhabitant, insistent, instant, intermittent, irritant, lafontant, latent, mightn't, militant, mutant, noncombatant, nonexistent, omnipotent, patent, persistent, pollutant, potent, protestant, reluctant, repentant, resistant, resultant, self-consistent, surfactant, unimportant, unrepentant