I didn't make it, I rather found it, lol. It's a neat trick. Go to
http://inheritance.smfforfree3.com for a preview. Double-clicking any word will cause a window to pop up with the word's definition.
Does not require jQuery.
Headers:
<script src="http://www.websters-online-dictionary.org/js/define.js" type="text/Javascript"></script>
Footers:
<div class="tborder"><div class="windowbg"><center>Double-clicking any word will pop out a window with it's definition. Click <a href="http://www.websters-dictionary-online.org/searchbox.asp">here</a> to learn how to do that.</center></div></div>
The footers thing is optional but I'd prefer it if you use it. It will tell your members about the dictionary and also give credit to the right party.