Doubtful rhymes with:
artful, boastful, deceitful, delightful, disrespectful, distasteful, distrustful, eventful, fateful, fistful, fitful, forgetful, fretful, frightful, fruitful, grateful, hateful, hurtful, insightful, lustful, mistrustful, neglectful, regretful, resentful, respectful, restful, rightful, self-fruitful, spiteful, tactful, tasteful, thoughtful, uneventful, ungrateful, wasteful, westphal, wistful, zestful