This offline Korean dictionary app looks helpful: https://play.google.com/store/apps/details?id=com.dictionary.ko&hl;=en

Endic.naver.com is perfectly suitable. No need for romanization. That's counterproductive. Daum is good too.

@Helen Thank You very much. I've already learned Korean Alphabet. because I am trying to learn vocabularies through K-drama's.I need such a dictionary. Do you know a good English-Korean Dictionary?

I don't think you should do that because a lot of the time people spell romanized Korean differently and/or incorrectly. I really suggest you learn the Korean alphabet! It's actually really easy and fast to learn! :)