A free app for Android, by Vedaist LLC.

Vedaist: English Dictionary is an educational and fun app for English learners. It helps you learn new vocabulary by offering you definitions, synonyms, examples, and idioms. You can search through a large database of over 900,000 words. 

As you browse through the results, you will find the definitions, synonyms, examples, and idioms in an easy-to-understand format. You can easily look up a word’s meaning on any topic or concept. The app includes a comprehensive search function that will allow you to search by word, by letter, or by example.

It is powered by Wikipedia sites for up-to-date definitions. It is a simple, intuitive, and beautiful app.