See our
Dictionary FAQ for instructions on creating a MOBI dictionary.
Question #6
Shouldn't be hard, once you have a tab-delimited dictionary.
Although that might take work.
Or you can do it the hard
er way by writing the XML yourself as susan_cassidy pointed you to.
Either way, it's going to be a lot harder than just converting an ordinary book.
P.S. You will need either mobpocket creator or kindlegen, because calibre doesn't support dictionaries.