Why
Part of speech: adverb
Definition: For what cause, reason, or purpose.
Part of speech: interjection
Definition: Exclamation of mild surprise.
Part of speech: noun
Definition: The reason.
Part of speech: conjunction
Definition: The reason that.
Example sentence: Ideas are more powerful than guns. We would not let our enemies have guns, why should we let them have ideas.
Wherefore
Part of speech: conjunction
Definition: Because of which.
Part of speech: adverb
Definition: Why, for what reason, because of what.Therefore.
Part of speech: noun
Definition: An intent or purpose.