Leibniz gave mathematicians and programmers their favourite word, but 'function' had been performing duties in English for over 150 years before he got to it. Latin fungi meant 'to perform' or 'to discharge' — a verb covering everything from executing an office to enjoying a right. Its noun form, functio, described the act of performing. Old French compressed this to fonction, and English adopted it in the 1530s to mean the proper activity or purpose of something. Organs had functions, officials had functions, ceremonies were functions. Then in 1694, Gottfried Wilhelm Leibniz needed a word for a mathematical concept: a quantity whose value depends on another quantity. He chose 'function,' and the technical sense took hold across European mathematics. By the twentieth century, computer science extended the meaning again: a function became a named block of code that performs a specific task. The word 'defunct' reveals the Latin root most clearly — something defunct has finished performing, its function discharged. 'Perfunctory' carries the same root but with a dismissive twist: performing a duty carelessly, just to get through it.