Dictionary Iphone with word list

Hello, I'm learning english and I need a usefull tool : an english dictionary that I can consultate with my Iphone. But I want two important specificities that I don't find.

Firstable, it has to be used offline. Prety easy to find, no probleme

Secondly, the most important, I need a word list with all the words I've already searched. Sort of interactive list that I can modify acording to the word I know or not.

Its so important in my mind!!

Thanks for help