arthritis definition by American Heritage Dictionary
Inflammation of a joint, usually accompanied by pain, swelling, and stiffness, and resulting from infection, trauma, degenerative changes, metabolic disturbances, or other causes. It occurs in various forms, such as bacterial arthritis, osteoarthritis, or rheumatoid arthritis.
Acute or chronic inflammation of one or more joints, usually accompanied by pain and stiffness, resulting from infection, trauma, degenerative changes, autoimmune disease, or other causes. See also osteoarthritis, rheumatoid arthritis.
top: healthy finger joint;
bottom: osteoarthritis in a finger joint showing inflammation of the synovial membrane and deterioration of the articular cartilage