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]

Moby Thesaurus II by Grady Ward, 1.0:

95 Moby Thesaurus words for "hypochondria":
   abstraction, abulia, accident neurosis, alienation, anxiety,
   anxiety equivalent, anxiety hysteria, anxiety neurosis,
   anxiety state, apathy, association neurosis, battle fatigue,
   blast neurosis, cachexia, cachexy, catatonic stupor,
   chronic ill health, combat fatigue, compensation neurosis,
   compulsion, compulsion neurosis, conversion hysteria,
   conversion neurosis, debilitation, debility, decrepitude,
   dejection, delicacy, delicate health, depression, detachment,
   elation, emotionalism, enervation, euphoria, exhaustion,
   expectation neurosis, feebleness, fixation neurosis,
   folie du doute, fragility, frailty, fright neurosis,
   healthlessness, homosexual neurosis, hypochondriasis, hysteria,
   hysterics, ill health, indifference, infirmity, insensibility,
   invalidism, invalidity, languishing, languishment, lethargy, mania,
   melancholia, mental distress, morbidity, morbidness, neurosis,
   neuroticism, obsession, obsessional neurosis,
   occupational neurosis, pathological indecisiveness, pathoneurosis,
   peakedness, phobia, poor health, preoccupation, psychalgia,
   psychasthenia, psychomotor disturbance, psychoneurosis,
   psychoneurotic disorder, psychopathia martialis,
   regression neurosis, shell shock, sickliness, situational neurosis,
   stupor, tic, twitching, unhealthiness, unresponsiveness,
   unsoundness, unwholesomeness, valetudinarianism, war neurosis,
   wasting, weakliness, withdrawal