According to TheFreeDictionary.com, the term "payor" is a legal term that refers to one who must make payment on a promissory note. The word "payer" is also used to describe the same function.
The term "payor," or "payer," derives from the Latin word "pac?re," which meant to pacify. In addition to being used as noun, "payor" can also be used as a verb to denote one is paying for something, such as a fine or service, or to note that one "pays for something" in metaphorical terms. The antonym of "payor" is "payee," which means "one to whom money is paid."