Source : Webster's Revised Unabridged Dictionary (1913)

Arthritis \Ar*thri"tis\ ([aum]r*thr[imac]"t[i^]s), n. [L., fr.
   Gr. 'arqri^tis (as if fem. of 'arqri`tis belonging to the
   joints, sc. no`sos disease) gout, fr. 'a`rqron a joint.]
   (Med.)
   Any inflammation of the joints, particularly the gout.

Source : WordNet®

arthritis
     n : inflammation of a joint or joints