Cecil used this word in his response to http://www.straightdope.com/classics/a5_154a.html
I can’t find this word in the OED, or any other dictionary. Did Uncle Cecil try to slip in a phoney word, thinking no one would notice?
Perhaps not phoney, but coined. Crepuscule means “twilight”, which is what Cecil seems to have added de- and -ate to. So I would say that decrepusculate means “bring out of the twilight” or more specifically, “illuminate”.
Q. What’s the difference between an optimist and a pessimist?
A. To an optimist, “to decrepusculate” means “to bring out of the twilight and into the light”. To a pessimist, it means “to bring out of the twilight and into the darkness”.
BWAHH HA HA HA HA HA HA!!
Q. What’s the difference between a compulsive polysyllabist and an average reader?
A. To a compulsive polysyllabist, “to decrepusculate” means, “Boy Howdy, I sure know some cool words.” To an average reader, it means, “This dink is firing over my head. I’ll skip this part.” The reader with perilously little knowledge of Greek and Latin might cobble together something about “removing crusty boils.” He would wonder why Cecil Adams would be glad to offer that service.
But of course, the “average reader” doesn’t read the Straight Dope.
Besides, knowledge of Italian will do – just think of Ricardo Wagner’s famous opera, “Il Crepuscolo degli Dei”, which you’ll find on the back of any opera score published by Riccordi.