arthritis (n.)

"inflammation of a joint," 1540s, from medical Latin arthritis, from Greek (nosos) arthritis "(disease) of the joints," from arthritis, fem. of arthrites (adj.) "pertaining to joints" (Greek nosos is a fem. noun), from arthron "a joint," from PIE root *ar- "to fit together." The older noun form was arthetica (late 14c.).