/ ˈbɜːsə; NAmE ˈbɜːrsə/ noun
( pl. bur·sae / -siː; NAmE / or bur·sas ) ( anatomy ) a part inside the body like a bag or sleeve, which is filled with liquid, especially around a joint so that it can work smoothly
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WORD ORIGIN
early 19th cent.: from medieval Latin , bag, purse , from Greek bursa leather.