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