that will make that facility available on almost any application.
I haven't tried them.
They probably won't work for DRM books, because they probably rely on copy and paste.
You'd need one that did OCR on the screen and then linked to a dictionary: not that hard to do but I don't know of one.
If you are a bit technical you could set up http://sourceforge.net/projects/capture2text/files/Capture2Text/ to do it.
An instant look-up dictionary would be a huge improvement for Digital Editions, especially since Digital Editions does not allow cut-and-paste which makes the conventional way of looking up words awkward.
An alternative solution would be for Digital Editions to allow the copying of single words of text. But providing instant dictionary look-up would be better.