It's not like payee, referee, etc., or not exactly. It is, of course, a noun formed from the past participle of the French verb employer = to employ. So un employé is a (male) person employed; une employée is a (female) person employed. These were originally both taken up into English and originally used the accent mark, which is now usually not used. There are others; divorce/divorcee come to mind. (I have to admit that I don't believe I've ever seen the masculine form of divorcee more than once and I don't believe I would ever use it.)