I’m going to expand on this list, but here are some vocabulary building apps that have been recommended.
https://itunes.apple.com/gb/app/free-exam-vocabulary-builder/id319052551?mt=8 https://play.google.com/store/apps/details?id=com.wordLearner.Free&hl=en https://itunes.apple.com/us/app/word-learner-owl/id587998206?mt=8 http://appcrawlr.com/ios/vocabology-word-of-the-day
http://www.knoword.org/
