>>Close to zero. Just another example of logic vs history - words which would be antonyms by construction often aren't even related. Cf. barred vs disbarred.
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>BTW, do you listen to Will Shortz and the Puzzle on Weekend Edition Sunday? He did one like that a week or two back. It was words where you could add "co" at the front and get totally unrelated words.

From time to time I do, and it's quite interesting. I can even guess it right occasionally, although I still don't have the proper mindset for a language with a non-phonetic script.