A family of Microsoft word processing software products for creating web, email, and print documents.
Since no one who has a real answer has tackled this, I'll tell you how I would handle this if I wanted a legal dictionary.
First, I would search online and see if there was one available commercially. If it wasn't to expensive I would get that.
http://www.e-medtools.com/openmedspel.html
Otherwise, I would look for a plain text list of terms. I would put them, 100 or so at a time, into a Word document. I would create a custom dictionary, set that as the default and add them to the dictionary.