What is any sac or saclike cavity; especially, one of the synovial sacs, or small spaces, often lined with synovial membrane, interposed between tendons and bony prominences called?

bursa — Any sac or saclike cavity; especially, one of the synovial sacs, or small spaces, often lined with synovial membrane, interposed between tendons and bony prominences. (Webster's 1913.)

Sources