The Collaborative International Dictionary of English v.0.48:

Rheumatism \Rheu"ma*tism\, n. [L. rheumatismus rheum, Gr. ????,
   fr.??? to have or suffer from a flux, fr. ??? rheum: cf. F.
   rheumatisme. See 2d Rheum.] (Med.)
   A general disease characterized by painful, often multiple,
   local inflammations, usually affecting the joints and
   muscles, but also extending sometimes to the deeper organs,
   as the heart.
   [1913 Webster]

   Inflammatory rheumatism (Med.), acute rheumatism attended
      with fever, and attacking usually the larger joints, which
      become swollen, hot, and very painful.

   Rheumatism root. (Bot.) See Twinleaf.
      [1913 Webster]

WordNet (r) 3.0 (2006):

rheumatism
    n 1: any painful disorder of the joints or muscles or connective
         tissues
    2: a chronic autoimmune disease with inflammation of the joints
       and marked deformities; something (possibly a virus) triggers
       an attack on the synovium by the immune system, which
       releases cytokines that stimulate an inflammatory reaction
       that can lead to the destruction of all components of the
       joint [syn: rheumatoid arthritis, atrophic arthritis,
       rheumatism]

Moby Thesaurus II by Grady Ward, 1.0:

131 Moby Thesaurus words for "rheumatism":
   adenoiditis, adrenitis, appendicitis, arteritis,
   arthritis deformans, arthritis fungosa, arthritis pauperum,
   atrophic arthritis, atrophic inflammation, blennorrhagic arthritis,
   brain fever, bronchitis, bunion, bursitis, capillaritis, carditis,
   catarrh, catarrhal inflammation, cerebellitis, cerebral meningitis,
   cerebritis, cerebrospinal meningitis, chronic infectious arthritis,
   chronic inflammation, cirrhotic inflammation, climactic arthritis,
   clitoritis, colitis, collagen disease, conjunctivitis, cystitis,
   degenerative arthritis, diffuse inflammation, encephalitis,
   endocarditis, enteritis, equine encephalomyelitis,
   exudative inflammation, fibroid inflammation, focal inflammation,
   gastritis, gingivitis, glossitis, gonococcal arthritis,
   gonorrheal arthritis, gonorrheal rheumatism, gout, gouty arthritis,
   hemophilic arthritis, hepatitis, hyperplastic inflammation,
   hypertrophic arthritis, hypertrophic inflammation,
   infectional arthritis, infectious hepatitis, inflammation,
   irritable bowel syndrome, laryngitis, lumbago, lumbar rheumatism,
   mastoiditis, meningitis, menopausal arthritis,
   metastatic inflammation, metritis, milk leg, mucous colitis,
   mumps meningitis, myelitis, necrotic inflammation, nephritis,
   neuritis, obliterative inflammation, ophthalitis, ophthalmia,
   orchitis, osseous rheumatism, osteitis, osteoarthritis,
   osteomyelitis, otitis, ovaritis, paradental pyorrhea, penitis,
   pericarditis, periodontitis, peritonitis, pharyngitis, phlebitis,
   podagra, proliferative arthritis, prostatitis, pyonephritis,
   pyorrhea, pyorrhea alveolaris, reactive inflammation, rheumatiz,
   rheumatoid arthritis, rhinitis, sclerosing inflammation,
   seroplastic inflammation, serous inflammation, serum hepatitis,
   simple inflammation, sinusitis, spastic colon,
   specific inflammation, subacute rheumatism, suppurative arthritis,
   suppurative inflammation, syphilitic arthritis, tennis elbow,
   testitis, thrombophlebitis, tonsilitis, torticollis,
   toxic inflammation, traumatic inflammation, tuberculous arthritis,
   tuberculous rheumatism, ulcerative colitis, uratic arthritis,
   ureteritis, urethral arthritis, urethritis, uteritis, vaginitis,
   vertebral arthritis, visceral rheumatism, vulvitis, wryneck