What does “마음속” mean in Korean?

Korean has two words for “inside.” 안 marks the plain interior of a space — inside a room, inside a bag. 속 goes deeper: the buried, packed, emotional inside. So 마음속 (maeumsok) isn’t merely “in the mind” — it’s someone lodged deep in the heart, where feelings hide. Attach 속 to other nouns and that same “deep within” shading carries over.

The confrontation lands on “이우진 마음속에 있는 여자?” — “the woman inside Lee Woojin’s heart?” Note the choice of 마음속 over 마음 안: 속 often feels deeper and more internal than 안, leaning toward something submerged and hidden — exactly the note the accusation strikes. 안 reads as a more neutral “inside,” so 마음 안 isn’t wrong, just less loaded. 속 is a native-Korean bound noun that fuses onto its noun as one word: 물속 (underwater), 꿈속 (in a dream), 숲속 (deep in the forest), 뱃속 (in one’s belly — and figuratively, one’s true intentions). The pattern is productive, so once you hear 속 you can read the “deep inside / concealed within” nuance across new compounds.