같이 등산 가기로 한 사람이 안 나왔어요. => The person who's supposed to go mountain hiking with me didn't show up. - 같이 등산 가다 = go hiking together (with me). * 등산 = mountain hiking/climbing. - 같이 등산 가기로 하다 = agree/promise/arrange to go hiking together (with me). - 같이 등산 가기로 한 사람 = the one who agreed/promised to go hiking together (with me). - 안 나오다 = 안(not) + 나오다(come out, appear in a program/show, show up at an appointment/meeting).