아깝다 means 1. unwilling to spend (something) ex) 그녀는 먹는 데 쓰는 돈을 아까워했다 She begrudged the money she spent on food. 이 신발은 버리기 아깝다 These shoes are still too good to throw away. 2. regrettable, pitiful ex) 경치가 너무 아름다워서 혼자 보기가 아까웠다 The scenery was so beautiful that it was a waste to be seeing it alone. 그렇게 어린 나이에 세상을 뜨다니 너무 아깝다 It's such a shame that he died so young. 아쉽다. means 1. sorry, sad ex) 이렇게 헤어지려니 너무 아쉽네요 It's too bad we have to part like this. 그가 없어서 못내 아쉬웠다 I felt something great was missing because he wasn't there. 2. feel the lack of (something) ex) 그 당시에는 돈이 아쉬웠다. Money was short at that time. 그는 아쉬울 때만 나를 찾는다 He looks for me only when he needs something.

덕분에 좋은 것을 배웠습니다. 좋은 질문을 하셨습니다, 러비님. (루비가 맞는지 럽비가 맞는지...) 감사합니다.