Is the word all a noun?

No, "all" is not typically a noun. It's usually used as a determiner or pronoun.

Here's why:

* Determiner: "All" modifies a noun, indicating the entire quantity or number. For example, "all the books," "all the people."

* Pronoun: "All" can stand in for a noun, referring to a previously mentioned group or quantity. For example, "I saw all of them."

While there are some rare cases where "all" could be considered a noun (like in phrases like "all is lost"), it's not its primary grammatical function.