걱정하다
geokjeonghada · TOPIK 1
to worry
걱정 (worry) + 하다 (to do) = to do worry
걱정 is the noun worry; 하다 is the all-purpose verb to do, which turns nouns into verbs. Same pattern as 공부하다 (study + do) and 운동하다 (exercise + do). Drop 하다 and you have the noun: 걱정 마 = no worries.