Definition of Royal Mail in US English:

Royal Mail

noun

  • 1(Frequently with the) a coach or (occasionally) other vehicle used by the British General Post Office to carry letters, parcels, etc. (now historical).

  • 2(A trademark for) the national postal service of the United Kingdom; now also the name of the company which provides this service.

Origin

Late 18th century; earliest use found in Chester Directory & Guide.