Here are some useful link that will help you improve your word knowledge. You can find links for dictionary websites, popular dictionary apps, mnemonics websites and many more.
Dictionary Websites (For Computer)
3. Word Web
Dictionary Apps (For Mobile)
4. Word web App
Mnemonics Websites
2. Membean
5. Word Reference (To find root words)
Vocabulary Building Games (APPs)
1. Vocabulary Builder (Magoosh)
Verbal and Communication Skills Lab 