The Encyclopedic Dictionary of Mathematics (http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=7771) sounds closest, at the level of MO. It is two volumes, and is of Japanese origin. The Springer Encyclopaedia of Mathematics, all online now at http://eom.springer.de/, is an updated version of a Soviet work. Neither of these, however, is going to be a good reference for discrete mathematics. I'm not aware of a book that does what you ask.