To affect with pain or uneasiness, either physical or mental; to trouble; to be the matter with; - used to express some uneasiness or affection, whose cause is unknown; as, what ails the man? It is never used to express a specific disease. We do not say, a fever ails him; but, something ails him. To be affected with pain or uneasiness of any sort; to be ill or indisposed or in trouble. Indisposition or morbid affection.