What part of speech is why?

"Why" can be a few different parts of speech, depending on its function in a sentence:

* Interrogative Adverb: When asking a question.

* Example: Why are you late?

* Conjunctive Adverb: When introducing a clause that explains a reason.

* Example: The car wouldn't start, why I was late.

* Noun: When it refers to the reason itself.

* Example: I want to know the why behind your decision.

Let me know if you'd like more examples!