The Collaborative International Dictionary of English v.0.48:

Hypochondrium \Hy`po*chon"dri*um\, n.; pl. L. Hypochondria, E.
   Hypochondriums. [L., fr. Gr. ?, from ? under the cartilage
   of the breastbone; ? under + ? cartilage.] (Anat.)
   Either of the hypochondriac regions.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Hypochondria \Hy`po*chon"dri*a\, n. [NL.] (Med.)
   An excessive concern about one's own health, particularly a
   morbid worry about illnesses which a person imagines are
   affecting him, often focusing on specific symptoms; also
   called hypochondriasis.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

hypochondria
    n 1: chronic and abnormal anxiety about imaginary symptoms and
         ailments [syn: hypochondria, hypochondriasis]