Definitions Bookmarklet - Select a word on a webpage, click the bookmarklet, and a new tab with Google's definition of the word will appear

DefinitionsBookmarklet.js

javascript:d=""+(window.getSelection?window.getSelection():document.getSelection?document.getSelection():document.selection.createRange().text);d=d.replace(/\r\n|\r|\n/g,"%20,");if(!d)d=prompt("Enter%20Word:",%20"");if(d!=null)location="http://www.google.com/search?q=define:"+escape(d).replace(/%20/g,"+");void(0);

If you want to use a different dictionary, replace http://www.google.com/search?q=define: and the formatting past it with the code needed to use your dictionary. Alternatively, you can search the internet to see if someone created one with your desired dictionary.