A medallion is a very large metal pendant that's given as an award. The medallion you won when you finished that marathon must be one of your most cherished possessions.
Medallions are extra big medals, discs of metal stamped with a design on both sides. When they're given to mark some achievement, medallions are often suspended from a ribbon that's hung around the recipient's neck or pinned to their clothing. Another kind of medallion is a small disc of boneless meat. And although most taxi drivers do deserve a medal, a taxi medallion is a permit to drive a cab.