Misunderstanding
noun, verbal noun
A mistake in what you solve... wow, sorry, I thought I was supposed to solve this, not that. What a terrible misunderstanding.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
君は誤解しているよ。あれは俺の姉貴だよ。
You’ve got the wrong idea. She’s my older sister.