"무서워, 두려워 and 겁나" - 무섭다: "be scared/fearful of something". Most common everyday word for fearing something. - 두렵다: "dread"(would rather avoid if possible). Sounds a bit literary, so is used less often in daily life. - 겁나다/겁이 나다/겁내다/겁을 내다: similar to 무섭다. Is often used in a slangy sense. * 무섭다/두렵다 is a simple adjective; 겁 나다/내다 (and 겁(을) 먹다) is a compound word, "have/express fear(겁)". * 옆집 개가 너무 무서워: I'm so scared of the dog next door. * 무서운 영화: scary movie, 무서운 괴물: scary monster. * 시험날 다가오는 게 두려워: I dread the test day approaching. * 누구나 죽음을 두려워한다: Everyone dreads death. * 시험에 떨어질까 봐 겁이 나 [겁나]: I fear failing the exam. * 물에 들어가는 걸 겁내지 마: Don't be scared of going in the water. * 그는 겁먹은 얼굴로 상대를 봤다: He looked at his opponent with a fear on his face. 두렵다 is never used in any slangy sense. 무섭다 has an extended sense of "tough, evil": 무서운 세상(a tough world), 무서운 인간(an evil man). 겁나다 often means "greatly / amazingly" too usually in 겁나게 form, with a slangy, exaggerated feel: - 그 친구(는) 축구를 겁나게 잘 해: He is amazingly good at soccer. - 사람들이 겁나게 많이 왔어: Frighteningly many people came. - 비가 겁나게 와: It's pouring like crazy.