At nearly 22,000 pages, weighin' close to 140 pounds in aggregate, definin' over 600,000 words (the average well-educated adult will have a vocabulary - or at least will recognize and understand - something in the vicinity of 40-60,000 words, a 100,000 word vocabulary is extraordinary, and typical day-to-day conversation employs approximately 4 to 6000 words), the 20 volume OED SE is gonna be damned hard to surpass if one is lookin' for a unified, comprehensive, authoritative repository, arbiter, and record of The English Language. Among other amazin' things, the OED offers just under 50,000 main entries for "obsolete" words.
Another bit of lexicological trivia; if entry-length is the measure, the verb "
set", scorin' well over 400 senses or definitions through some 60,000+ words (roughly equivalent to the word count of a 250-page novel) would be the most "defined" word in the English language