What part of speech is the word leaving?

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

* Verb: This is the most common use. For example: "He is leaving for work."

* Gerund: This is when it acts as a noun. For example: "Leaving early was a mistake."

* Participle: This is when it acts as an adjective. For example: "The leaving train was crowded."

To determine the specific part of speech, you need to look at its function in the sentence.