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 that has been left in 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.” Formally, it is called a retained surgical sponge, an example of the more general class of retained foreign objects.
In both subject and appearance, gossypiboma surely fits anybody’s definition of a weird word. Online dictionaries have said that 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 boma is a raised enclosure of some sort, especially for protective or defensive purposes (it’s from a Persian or Farsi word for a garrison or a place of safety). This is surely a false etymology.
It is much more likely that gossypiboma was created 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. This derivation is supported by another word for the situation, textiloma (from textile plus -oma), coined in 1996 in a paper in the Journal of Computer Assisted Tomography by a German radiologist, Lars Kopka, and four of his colleagues. Since surgical sponges are now usually made of synthetic fabrics it’s more appropriate than gossypiboma and is becoming the more frequently used word.
The earliest known example of gossypiboma was found by subscriber David Hocken in the title of an article in the journal Radiology in November 1978: Gossypiboma: The problem of the retained surgical sponge.