착각이 · 착각을
mistaken belief, illusion, confusion
Example
오늘이 일요일인 줄 알고 잠깐 착각했어요.
I briefly got confused and thought today was Sunday.
Word parts
착 mistaken+각 perceive
Literally 'mistaken perception'.
Good to know
Pattern: -(으)ㄴ/는 줄 착각하다 'mistakenly think that …'.