How about words that are not rare, but used infrequently enough that many people forget them, such as "eleemosynary"? ...It was The Word for Today about six years ago. Does that disqualify it?

no, that wouldn't disqualify it -- I steal words from all over. but I used eleemosynary as a wwftd in Nov. 1994; *that disqualifies it (at least for now). :)