The most common Korean word for “sky” is 하늘 (haneul). 「sky」는 한국어로 하늘.
Learn 하늘 free — flashcards, audio and review →「하늘」 단어장으로 무료로 외우기Words and levels: TOPIK I essentials (National Institute of Korean Language standard curriculum, KOGL Type 1) · examples: Cheesepotato