postal service is a noun meaning "the system whereby messages are transmitted via the post office". It carries one recorded sense.
the system whereby messages are transmitted via the post office
“the mail handles billions of items every day”
“he works for the United States mail service”
“in England they call mail `the post'”
Definitions, synonyms and semantic relations for postal service come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.