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