A perfunctory explanation of the origins of perfunctory would be this: it comes from Latin. Borrowed in the late 16th century, the word is specifically from the Late Latin perfunctorius, meaning "done in a careless or superficial manner." Perfunctorius ultimately comes from two Latin sources, per-, meaning "through," and fungi, meaning "to perform." Fungi is also a source to such words as function, defunct, and fungible, but not to fungus; that word is also from Latin, but it is most likely a modification of the Greek word spongos, meaning "sponge."