Can the word on be a noun?

Yes, "on" can be a noun in certain contexts. It's often used in these ways:

* As a shortened form of "the one": "He's the on to watch."

* To refer to a particular thing or person: "I'm on the lookout for a new phone."

* In phrases like "the on-call team" or "the on-site manager": "The on-call team is ready to respond."

* To refer to an action or state: "The party's on."

It's important to note that these usages are less common than "on" being used as a preposition. If you're unsure whether "on" is functioning as a noun in a particular sentence, consider its meaning and context.