I started using WordWeb about ten years back. It is a small nifty app for Windows which has a built in Thesaurus/Dictionary. Over the years I have considered it a must have application on my PC. It helps me when I am writing. The choice of words presented is impressive. Now it is even available for Android smart-phones.
It is totally free, takes 22 Mb of space and works with Android versions 2.2 and up. The Windows version of WordWeb can be downloaded here. If you use Android smart-phone you can it install from here. It can show examples, synonyms, antonyms, similar words, types and derived words etc. You can also make regional settings for American, Australian, British or Canadian English versions. The font size can be changed from settings and you can also set exclusions to show vulgar/offensive words. Also one can search for words using the built in search facility. Bookmarks can be set and recent words can also be viewed. I think it is a very good app to have. Please do try it out.