Dictionary.net

A morbid concern about the health and exaggerated attention to any unusual bodily or mental sensations; an unfounded belief that one is suffering from some disease.

Slight melancholy, fear of illness, etc.

A form of insanity in which the patient converts an idea of purely mental origin into what appears to him to be a real material change.

This disease is probably so called, from the circumstance of some hypochondriacs having felt an uneasy sensation in the hypochondriac regions. The disease seems really to be, as Pinel has classed it, a species of neurosis, and of mental alienation, which is observed in persons who in other respects are of sound judgment, but who reason erroneously on whatever concerns their own health. Hypochondriasis is characterized by disordered digestion, without fever or local lesion; flatulence; borborygmi; extreme increase of sensibility; palpitations; illusions of the senses; a succession of morbid feelings, which appear to simulate the greater part of diseases; panics; exaggerated uneasiness of various kinds; chiefly in what regards the health, etc. Indigestion has usually been considered the cause of hypochondriasis. They are, unquestionably, much connected with each other: but there is every reason to believe, that the seat of the affection is really, though functionally, in the brain. The disease almost always appears at the adult age, most commonly in irritable individuals; and in those exhausted, or rather in the habit of being exhausted by mental labour, overwhelmed with domestic or public affairs, etc. The treatment is almost entirely moral. The condition of the digestive function must, however, be accurately attended to.

Morbid anxiety about the health.

Persistent anxiety about health with exaggeration of small bodily symptoms. The mental condition takes its name from the hypochondriac region, to which feelings of distress and uneasiness were previously referred. [Gr.]