Is the word tirelessly a noun?

No, "tirelessly" is an adverb. It describes how an action is performed (without tiring).

Here's a breakdown:

* Noun: A word that names a person, place, thing, or idea (e.g., "dog," "house," "freedom").

* Adverb: A word that modifies a verb, adjective, or another adverb, telling us how, when, where, or to what extent something is done (e.g., "quickly," "happily," "very").

In the sentence "She worked tirelessly on the project," "tirelessly" tells us how she worked.