Both are very different ones. 중요하다 comes quite close to "important" in English, thus no further explanation needed. 중하다 on the other hand means "serious", "crucial", "vital", "severe", "critical", etc. 중(重) literally means "heavy". e.g. 이 환자는 상태가 중하다. This patient is in a critical status. 중환자: critical/serious patient. 중대사: crucial matter 중공업: heavy industry 중장비: heavy equipment 중상: heavy injury It's antonym is 경(輕): light Now you know tons of other words derived from those above: 경공업 경장비 경상

특별한 차이는 없어요. "중요하다"는 흔히 쓰이는 말이고 "중하다"는 평소에 잘 쓰지 않는 말입니다. 옛날 느낌을 주는 말이에요. 참고로 작년경에는 '뭣이 중헌디 !! ' 라는 유행어가 있었습니다. 중요하다 is commonly used while 중하다 is old and not used very much, Especially young people don't use anymore 중하다 because it sound quite out-dated and too formal. But the phrase '뭣이 중헌디' was very popular last year. It came from a movie. (I didn't watch it..)