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]