The Collaborative International Dictionary of English v.0.48:

Indigestion \In`di*ges"tion\ (?; 106), n. [L. indigestio: cf. F.
   indigestion. See In- not, and Digest.]
   Discomfort due to a lack of proper digestive action; a
   failure of the normal changes which food should undergo in
   the alimentary canal; dyspepsia; incomplete or difficult
   digestion.
   [1913 Webster]

WordNet (r) 3.0 (2006):

indigestion
    n 1: a disorder of digestive function characterized by
         discomfort or heartburn or nausea [syn: indigestion,
         dyspepsia, stomach upset, upset stomach]

Moby Thesaurus II by Grady Ward, 1.0:

83 Moby Thesaurus words for "indigestion":
   abscess, ague, anemia, ankylosis, anoxia, apnea, asphyxiation,
   asthma, ataxia, atrophy, backache, bleeding, blennorhea, cachexia,
   cachexy, cardialgia, chill, chills, cholera morbus, colic,
   constipation, convulsion, costiveness, coughing, cyanosis,
   diarrhea, dizziness, dropsy, dysentery, dyspepsia, dyspnea, edema,
   emaciation, fainting, fatigue, fever, fibrillation, flux, gripe,
   gripes, growth, heartburn, hemorrhage, high blood pressure,
   hydrops, hypertension, hypotension, icterus, inflammation,
   insomnia, irregularity, itching, jaundice, labored breathing,
   lientery, low blood pressure, lumbago, marasmus, nasal discharge,
   nausea, necrosis, obstipation, pain, paralysis, pruritus, pyrosis,
   rash, rheum, sclerosis, seizure, shock, skin eruption, sneezing,
   sore, spasm, tabes, tachycardia, trots, tumor, upset stomach,
   vertigo, vomiting, wasting



The Devil's Dictionary (1881-1906):

INDIGESTION, n.  A disease which the patient and his friends
frequently mistake for deep religious conviction and concern for the
salvation of mankind.  As the simple Red Man of the western wild put
it, with, it must be confessed, a certain force:  "Plenty well, no
pray; big bellyache, heap God."