1. (v. t.) 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? I know not what ails him.

2. (v. i.) To be affected with pain or uneasiness of any sort; to be ill or indisposed or in trouble.

3. (n.) Indisposition or morbid affection.