The most common Korean word for “fun” is 재미있다 (jaemiitda). There is one more word with a similar meaning — compare them below. 「fun」는 한국어로 재미있다.
to be fun; interesting
TOPIK 1 · adjective
Words and levels: TOPIK I essentials (National Institute of Korean Language standard curriculum, KOGL Type 1) · examples: Cheesepotato