WordWeb is a dictionary (and Thesaurus) where you can lookup any word virtually from any program. I have been using it for years. I know you can google words to get their definitions, but it is nice to have a dictionary available, even when you are not online.
WordWeb can be installed as a portable app too (just click on the “advanced options” during the install process). WordWeb recently received some suttle updates (such as new words and spelling suggestions).
Another really cool feature built into WordWeb is the ability to use Wikipedia, Wiktionary and WordWeb online. If you do not have WordWeb, I suggest you get it [HERE]