Lexicon uses Wiktionary to look up words. The very first time you access a word you need to have internet connection. Lexicon saves the word in an internal database so you don't have to access the web on any subsequent call to the same word. Having said that, the only permission Lexicon asks from your device is internet connection.
Lexicon prefers to be installed in an external SD card (if you have any, otherwise it installs in your device's main memory).
Lexicon is tested and works with the following applications:
Maxthon Mobile Browser
It might work for other devices too, but I can't gurantee it since I've noticed that some of them send specialised content with the selected text.
If you want to see Lexicon work for other applications (not listed above) or for any questions/suggestions/bugs please contact me.