Wouldn't that be "magnum opus?" My quibble was with "de jure," a Latin phrase that is jarringly out of context with his thread. I assumed he meant the French "du jour," which means "daily." So the
nom -- if I'm correct -- would have been "Greatest work of the day." Which makes more sense than some legal babble.
On the other hand, I've wasted far too much time on this already, so I'll let the thread survive or fail on its own merits, linguistic puzzles unresolved.