postal service vs communication

postal service and communication both are nouns.

Word	Noun	Adjective	Verb	Adverb
postal service	Yes	No	No	No
communication	Yes	No	No	No

As nouns, communication is a hypernym of postal service; that is, communication is a word with a broader meaning than postal service:

postal service: the system whereby messages are transmitted via the post office
communication: the activity of communicating; the activity of conveying information

Other hypernyms of postal service include communicating.

postal service (noun)	communication (noun)
the system whereby messages are transmitted via the post office	something that is communicated by or to or between people or groups
	the activity of communicating; the activity of conveying information
	a connection allowing access between persons or places