Hi Dale. I wonder what you consider a "usu dictionar[y]." I've done a brief check and, so far, AHD, MWO, Encarta, COED, Cambridge International and dictionary.com all give the generic meaning, something along the lines of "something that achieves sudden, unexpected success." Perhaps it's the lack of your proffered definition, "anything ordinary on the outside but extraordinary inside" which is more like a definition for "ringer" than for "sleeper."