A prehistoric mammal that was overly fond of chocolate, creme-filled sandwich cookies.
Or, if you'd rather listen to the OED, "A former genus (now included in the genus Merycoidodon) of extinct pig-sized ruminantmammals of the family Oreodontidae, having four toes on each foot and selenodont teeth, the remains of which are found in Middle Tertiary rocks in the western United States; (also) an animal of this genus. Later chiefly in Oreodon beds: strata containing fossils of these animals."
Isn't the cookie definition better, now? Be honest. And consider the fact that "Most researchers in paleobiology and paleontology now use the antecedent genus Merycoidodon to refer to this Oligocene epoch oreodont. The name "Oreodon" is actually a synonym of the fish genus Orodus, and is, thus, not a valid scientific name." (Wikipedia)