bursa
Concise Oxford English Dictionary © 2008 Oxford University Press:
bursa /ˈbəːsə/
▶noun (pl. bursae /-siː/ or bursas) Anatomy a fluid-filled sac or cavity, especially one countering friction at a joint.
– derivatives
bursal adjective.
bursal adjective.
– origin C19: from med. L., ‘bag, purse’.
'bursa' also found in these Oxford entries:

