Yeah, it worked for me for some terms the day I downloaded it; when I went back for more, I got the same result: terms listed, without definitions. I have no idea what changed.
If the original author will please step forward, I’m sure we could get to the bottom of it. I suspect the file is somehow illegitimate. Why else is it hosted on mediafire and doesn’t show up with common search queries?
Sadly, it appears that all free medical dictionaries for Mac today are either simple word lists for spell checking only, or are web-based and often ad-supported. Windows and Google Chrome and Handheld (Palm, PocketPC) options exist, but nothing that integrates with the Dictionary.app on Mac OS X.
A truly free medical dictionary would be great; once the content is created, then making a dictionary compatible with Apple’s Dictionary.app would be trivial. Until then, I guess $50 or $55 is a reasonable price … if it fits with your current digital workflow.