It's important to note that "nay" is actually a Middle English word, derived from Old English "nā". In Old English, "nā" was used both as a stand-alone word meaning "no" and as a negative particle similar to "not".
Here are some examples:
* "Nā, ic ne wāt." (Old English) - "No, I do not know."
* "Hē nā cōm." (Old English) - "He did not come."
In modern English, "nay" is often used in formal or archaic contexts to add a sense of seriousness or solemnity.