rheumatism (n.)

c. 1600, from Late Latin rheumatismus, from Greek rheumatismos, from rheumatizein "suffer from the flux," from rheuma "a discharge from the body" (from PIE root *sreu- "to flow"). "The meaning of a disease of the joints is first recorded in 1688, because rheumatism was thought to be caused by an excessive flow of rheum into a joint thereby stretching ligaments" [Barnhart].