A metonym is a word that names an object from a single characteristic of it or of a closely related object.
- The White House released its official report today. — "The White House" for "The presidential administration"
- The Crown has enacted a new social security policy. —"The Crown" for "The government of the United Kingdom".
- A crowd of fifty heads —where "head" stands for person.
- Put it on the plastic — material (plastic) for object (credit card)