Another C# app I wrote ages ago that I still use on every single one of the machines I use.  Wordy lives in the tray and provides a quick way of looking up a word's definition.  I use this at least a couple of times a day as my vocabulary has never been a strong point. 

Ways to look up a word:

• Copy a word to the clipboard and double-click the Wordy icon in the system tray.
• Right-click the Wordy icon in the system tray and select “Look up a word“.  A dialog will appear asking you to provide the word you want to look up.

Download: [Executable] --- [Source]

If you're interested in the straight Win32 version of the app, you can download the executable for it from here.  I have no idea where the source is for that version anymore, so binaries will have to do for now.