Actually, I don't know of one. I assumed that using one would require a minimum of 20 or more button pushes per look-up and that's if I was lucky at guessing a word's location in the dictionary. So I haven't bothered to try to find one. However, there is a thread here about a dictionary for the Sony Readers that involves a hack. You might read through and decide if it's something for you to try or not:
https://www.mobileread.com/forums/showthread.php?t=22320