public speaker vs talker

public speaker and talker both are nouns.

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

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

public speaker: a person who delivers a speech or oration
talker: 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 speaker, utterer, verbaliser, verbalizer.

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