n., as used in Love Story (written by Erich Segal, made in the early '70s)-- a "preppy"/"preppie" is one who is preppy.
adj., old money, classy, conservative, tasteful. See several definitions above: private schools and first-class colleges or legacies at colleges. Philanthropy is also valued. As far as clothing goes, these days it's mainly Polo, Burberry, Lacoste, Brooks Bros., L.L. Bean, etc. Preppiness is usually found on the East Coast, most often... it seems that several people are limiting it to New England, which is not right. I have enough friends from Richmond and Raleigh and New Orleans and Atlanta to tell you that preppiness is alive and well in the South-- it's often almost exaggerated down here.
n.-- Charlotte grew up a preppy, shunning her family's new-money, money-wasting ways.
adj.-- Hunt looked rather preppy in his duck boots sans socks and his Nantucket Reds shorts.