public address system vs speaker

public address system and speaker both are nouns.

Word	Noun	Adjective	Verb	Adverb
public address system	Yes	No	No	No
speaker	Yes	No	No	No

public address system (noun)	speaker (noun)
an electronic amplification system used as a communication system in public areas	electro-acoustic transducer that converts electrical signals into sounds loud enough to be heard at a distance
	someone who expresses in language; someone who talks (especially someone who delivers a public speech or someone especially garrulous)