I like LDC's variant on the idea. The original (public domain) version could be held sacrosanct. Visitors could leave commentary, add new meanings, and even add new words. (I don't think any public domain dictionaries will have a definition of the word 'sendmail', for example.) But the new stuff would always appear slightly separated from the original.
I don't think this should be a "ghetto" for too-short wikipedia entries, but a separate thing. And I think that the software should be as simple and easy to use as wiki software, but made especially for this project.
I could write a super simple version pretty quickly.
Does anyone know where I can get a sensibly-delimited public domain dictionary to get started? I know that one exists somewhere.
--Jimbo