Even matching a WikiWord is a bit tricky. Topic pages are stored as text, markup is added dynamically when the page is called, so there's nothing in the topic itself to show whether or not a topic is populated.

I've played with a couple of formatted searches to return a list of WikiWords, but even that's a bit of a trick.

Remotely fetching the tree and looking for nonrendered WikiWords might be another tack, but I don't think that's what you're looking for.

The [link|http://twiki.org/cgi-bin/view/Codev/ListingAllUndefinedButUsedWikiWords|definitive answer] appears to be "that's an interesting question, work in progress".