The adjective rheumatic describes anything having to do with rheumatism, a painful disease of the joints. If your grandfather moves slowly, you could describe him as rheumatic.
You could describe a doctor as "a rheumatic expert," or a patient as moving in a rheumatic way, slow and arthritic. The Latin root word is rheumaticus, "troubled with rheum," and rheum itself is a Greek word that means "flow." The word was first ascribed to the disease of rheumatism because of the way it seemed to spread — or flow — within a patient's body.