Source : Webster's Revised Unabridged Dictionary (1913)

Hypochondriasis \Hy`po*chon"dri*a*sis\, n. [NL. So named because
   supposed to have its seat in the hypochondriac regions. See
   {Hypochondriac}, {Hypochondrium}, and cf. {Hyp}, 1st {Hypo}.]
   (Med.)
   A mental disorder in which melancholy and gloomy views
   torment the affected person, particularly concerning his own
   health.

Source : WordNet®

hypochondriasis
     n : chronic and abnormal anxiety about imaginary symptoms and
         ailments [syn: {hypochondria}]