public speaker vs speaker

public speaker and speaker both are nouns.

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

As nouns, speaker is a hypernym of public speaker; that is, speaker is a word with a broader meaning than public speaker:

public speaker: a person who delivers a speech or oration
speaker: someone who expresses in language; someone who talks (especially someone who delivers a public speech or someone especially garrulous)

Other hypernyms of public speaker include talker, utterer, verbaliser, verbalizer.

public speaker (noun)	speaker (noun)
a person who delivers a speech or oration	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)