Improve your vocabulary with Voice of America’s Mobile Wordbook. It’s a free app for iOS and Android. Each word has a definition in English, synonyms, and example sentences. If you click on the volume button in the bottom right corner, you can hear the whole thing read in English (American accent). It’s not a very complete library (only two words in Z), but maybe it can encourage you to create your own index like this (multimedia!) in your portfolio.