1. A nervous disorder that is marked by continual slow movements especially of the extremities and is usually due to a brain lesion.
2. A derangement marked by ceaseless occurrence of slow, sinuous, writhing movements, especially severe in the hands and performed involuntarily, it may occur after hemiplegia and is then known as posthemiplegic chorea.
3. A condition, chiefly in children, of slow, involuntary, wormlike movements of the fingers, toes, hands, and feet, usually resulting from a brain lesion.
4. A constant succession of slow, writhing, involuntary movements of flexion, extension, pronation, and supination of fingers and hands, and sometimes of toes and feet.

Coined by the American nerve specialist William Alexander Hammond (1828-1900) in 1871 from Greek athetos, "not fixed" and suffix -osis, "a state of a disease".