Ammon Shea, who spent a year reading the Oxford English Dictionary from cover to cover and wrote about it in his book Reading the OED, commented on this word — meaning a surgical sponge left within a patient after an operation — in a piece on the OUPBlog. The surgeon who told him about it called it “a memento that we surgeons sometimes accidentally leave behind to commemorate our presence in some poor patient’s abdomen.”
In both subject and appearance, gossypiboma surely fits anybody’s definition of a weird word. Online dictionaries say it’s an amalgam of words from two languages: Latin gossypium, cotton, and Swahili boma, meaning a place of concealment. However, standard Swahili dictionaries say that boma is a raised enclosure of some sort, especially for protective or defensive purposes (it is from a Persian or Farsi word for a garrison or a place of safety). It may be that gossypiboma is just formed from the Latin word plus the ending -oma that denotes a tumour or other abnormal growth (as in carcinoma or lymphoma), with a b added to separate the vowels. The ending is appropriate, since such growths can develop around alien material left in the body.
Gossypiboma was said in a book on surgery in 2004 to have been coined in an article of 1994 by A M Patel and others. However, subscriber David Hocken, himself a doctor, has found a much earlier example, in the title of an article that appeared in the journal Radiology in November 1978: Gossypiboma: The problem of the retained surgical sponge.