P.A. vs public address system

P.A. and public address system both are nouns.

Word	Noun	Adjective	Verb	Adverb
P.A.	Yes	No	No	No
public address system	Yes	No	No	No

As nouns, P.A. and public address system are synonyms defined as:

P.A. and public address system: an electronic amplification system used as a communication system in public areas

Other synonyms of P.A. include P.A. system, PA, PA system.

P.A. (noun)	public address system (noun)
an electronic amplification system used as a communication system in public areas	an electronic amplification system used as a communication system in public areas