There are few gadgets and plug-ins for Urban Dictionary. But I don't know any that would work with your clipboard. Here is the one. Urban Dictionary Client will be running in background until you need it. Just select the word (or phrase) you want to translate, press Ctrl and they press C twice (ctrl-C-C). Features auto-update in case new features are added or bug fixed.
|File Size||507.65 kB|
|Operating System||Windows XP Windows 7 Windows Windows Vista|