ZIP It!

An article on the most expensive ZIP Codes in the country got me thinking about an age-old question: what does ZIP stand for? At a quiz night in Seattle with my dad a few years ago, I insisted that the acronym did not actually stand for anything. I was fairly certain it was a made up word. And that, my friends, would be an excellent trivia question. However the supposed answer was "Zoned in Postal," costing my dad and I an $85 payday (in Seattle, they play trivia for money. They also have blackjack facilities in residential neighborhoods. God, I miss that place). I never found verification on that one way or the other. Anyway, the aforementioned article provides the moronic statement that ZIP stands for "Zoning Improvement Code" which would really be a ZIC code. So that is clearly wrong. But Yahoo! claims that it stands for "Zoning Improvement Plan," which at least reduces to ZIP, so that's somethin'. And I guess they're on to something because the US Postal Service concurs. But this whole thing still smacks of a post hoc rationalization, to use a good Con Law phrase, and I still say that originally, it was a made up word that stood for nothing. Now, if I could only find something to back me up on this...