synovium

/sɪˈnoʊviəm/
noun
  1. The thin layer of tissue that lines the inside of a joint and produces fluid to lubricate and cushion the joint.
    • The synovium helps keep your knees moving smoothly by releasing lubricating fluid.
    • Doctors examined the synovium to check for signs of infection in the patient's hip.
    • In arthritis, the synovium can become inflamed and cause pain and swelling.