rheumatoid (adj.)

late 14c., reume, "watery fluid or humid matter in the eyes, nose, or mouth" (including tears, saliva, mucous discharge from the nostrils), from Old French reume "a head-cold" (13c., Modern French rhume) and directly from Latin rheuma, reuma, from Greek rheuma "discharge from the body, flux; a stream, current, flood, a flowing," literally "that which flows," from rhein "to flow" (from PIE root *sreu- "to flow").

In old medicine it was conceived as draining from the higher to lower parts of the body and causing ailments if out of balance. Also from late 14c. as "a head-cold, catarrh." The -h- was restored in early Modern English.

word-forming element meaning "like, like that of, thing like a ______," from Latinized form of Greek -oeidēs (three syllables), from eidos "form," related to idein "to see," eidenai "to know;" literally "to see" (from PIE *weid-es-, from root *weid- "to see"). The -o- is connective or a stem vowel from the previous element. Often implying an incomplete or imperfect resemblance to the thing indicated.

Proto-Indo-European root meaning "to flow."

It forms all or part of: amenorrhea; catarrh; diarrhea; gonorrhea; hemorrhoids; maelstrom; rheo-; rheology; rheostat; rheum; rheumatic; rheumatism; rheumatoid; rhinorrhea; rhythm; seborrhea; stream.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit sravati "flows," srotah "stream;" Avestan thraotah- "stream, river," Old Persian rauta "river;" Greek rhein "to flow," rheos "a flowing, stream," rhythmos "rhythm," rhytos "fluid, liquid;" Old Irish sruaim, Irish sruth "stream, river;" Welsh ffrwd "stream;" Old Norse straumr, Old English stream; Lettish strauma "stream, river;" Lithuanian sravėti "to trickle, ooze;" Old Church Slavonic struja "river," o-strovu "island," literally "that which is surrounded by a river;" Polish strumień "brook."