by 1788 as an English word in physiology, shortened from medieval Latin bursa mucosa "mucus pouch," from Medieval Latin bursa "bag, purse," from Late Latin bursa, variant of byrsa "hide," from Greek byrsa "hide, skin, wine-skin, drum," which is of unknown origin; compare purse (n.). Related: Bursal (1751).
word-forming element in medicine denoting "diseases characterized by inflammation" (of the specified part), Modern Latin, from Greek -itis, feminine of adjectival suffix -ites "pertaining to." Feminine because it was used with an implied nosos "disease," a feminine noun; especially in arthritis (nosos) "(disease) of the joints." Arthritis (16c.) was one of the earliest appearances of the suffix in English and from it the suffix was abstracted in other uses.
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Definitions of bursitis from WordNet
inflammation of a bursa; frequently in the shoulder;