PA vs communication system

PA and communication system both are nouns.

Word	Noun	Adjective	Verb	Adverb
PA	Yes	No	No	No
communication system	Yes	No	No	No

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

PA: an electronic amplification system used as a communication system in public areas
communication system: a system for communicating

PA (noun)	communication system (noun)
an electronic amplification system used as a communication system in public areas	facility consisting of the physical plants and equipment for disseminating information
a Mid-Atlantic state; one of the original 13 colonies, with capital Harrisburg	a system for communicating