What part of speech is the word millions?

"Millions" can be a few different parts of speech, depending on its context:

* Noun: When it refers to a large number of things, as in "There were millions of people at the concert."

* Adjective: When it modifies another noun, as in "Millions of dollars were spent on the project."

* Pronoun: This is less common but possible in certain contexts. For example, "Millions were affected by the storm."

The part of speech is determined by its role in the sentence.