Fatigue: A condition characterized by a lessened capacity for work and reduced efficiency of accomplishment, usually accompanied by a feeling of weariness and tiredness. Fatigue can be acute and come on suddenly or chronic and persist.

"Fatigue" is a favorite medical word. When a patient says they have been feeling unusually tired, "real tired," the doctor will usually write down that the patient presents with "fatigue."

See also: Chronic fatigue syndrome.