public relations vs promotion

public relations and promotion both are nouns.

Word	Noun	Adjective	Verb	Adverb
public relations	Yes	No	No	No
promotion	Yes	No	No	No

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

public relations: a promotion intended to create goodwill for a person or institution
promotion: a message issued in behalf of some product or cause or idea or person or institution

Other hypernyms of public relations include packaging, promo, promotional material, publicity.

public relations (noun)	promotion (noun)
a promotion intended to create goodwill for a person or institution	act of raising in rank or position
	the advancement of some enterprise
	a message issued in behalf of some product or cause or idea or person or institution
	encouragement of the progress or growth or acceptance of something