An ailment is an illness, but usually not a very serious one — a sore back, a stomach problem, a cough that will not quite go. Doctors, chemists, and newspapers like the word because it sounds a little more formal than illness and a little softer than disease. You will hear minor ailments, childhood ailments, and “an old ailment in his knee”. Though actually, people sometimes stretch it toward any bodily trouble, even when it has lasted for years; they still would not normally call cancer or a heart attack an ailment. It is built from the old verb ail, “to feel unwell”, plus -ment. You may also meet whatever ails you, which can mean any trouble at all, not only a medical one — but ailment itself stays mostly about the body.