Apple's Sherlock buttons didn't offer the functionality I missed most, from MerriamWebster.com's old javascript dictionary button. Written for older versions of Netscape or MSIE, the freely available button doesn't work with Safari. The nice thing about the button was that you could either highlight a word in a page and punch the button for lookup OR just punch the button and enter a word into a dialog box.
Some slight tinkering with that javascript produced the following -- enter it as one long line with no added spaces (just remove the line breaks):
javascript:x=escape(getSelection());if(!x)%7Bvoid(x=prompt
('Word?',''))%7D;window.location='http://dictionary.reference.com/
search?q='+x
Of course, you can replace the URL with your preferred dictionary site--but you may have to change the syntax a bit.

