What part of speech is check in?

"Check in" can be two parts of speech, depending on how it's used:

1. Noun: When referring to the act of registering at a hotel, airport, or other establishment, it is a noun.

* Example: "I completed the check-in process and got my room key."

2. Verb: When describing the action of registering or arriving at a place, it is a verb.

* Example: "Please check in at the front desk."

It's important to look at the context of the sentence to determine the correct part of speech.