Reason, Motive, Excuse
noun
A reason reason is a reason! How could it not be? Do you have a reason why it shouldn't be? I thought not. This word means "reason" as in the reason you're studying Japanese, or the reason you're late. That's why it can also mean similar words like motive and excuse.
りゆう
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
理由は有りません。
There is no reason.
休学の理由は不明です。
The reason for the leave of absence is unknown.
理由は分かりませんが、主人が今すぐ海外に行かなければいけないと言ってるんです。
I don't know why, but my husband says he has to go abroad right now.