What part of speech is complain?

"Complain" can be a few different parts of speech, depending on how it's used in a sentence:

* Verb: This is the most common usage. Example: "The customers complained about the slow service."

* Noun: This is less common, but it can be used to refer to the act of complaining. Example: "Her constant complains were starting to get on everyone's nerves."

Let me know if you'd like more examples!