Reason
noun
This word takes the reason meaning of the kanji, making it reason. What's the reason for it having two meanings? I have no clue, but there must be a reason.
While 理由 is the general term for reasons, 訳 tends to be more focused on the underlying reason or cause of something. It's also used when explaining a situation or when there's an implied need to justify or clarify something.
Since this word is made up of a single kanji, it probably uses the kun'yomi reading. You didn't learn this reading, so here's a mnemonic to help you:
What's your reason to wake (わけ) up this morning? Think about it. Now think of your reason to wake up tomorrow. What is it?
どうして便器の上で逆立ちをしようとしたのか訳を聞かせてください。
Can you tell me the reason why you tried doing a handstand over the toilet?