This app has everything you need! With definitions for literally thousands of words, giving the ability to handle the primary barrier to understanding: misunderstood words. There is a "voice-search" option. The lazy part of me likes this and it enables me to look up a word, even if I don't know the spelling.
There are over 1,000 illustration and over 20,000 entries, including people, places and foreign terms. I like the fact that sample sentences are given, which help you to understand the way the word is used as well as narrowing down the correct usage.
No internet connection is required in order to view definitions, but it is necessary for viewing illustrations, hearing audio pronunciations and voice search. It is worth every penny! There are free versions, but they are supported by ads.
Compatible with iPhone, iPad, and iPod touch.