precursor vs harbinger

precursor and harbinger both are nouns.

Word	Noun	Adjective	Verb	Adverb
precursor	Yes	No	No	No
harbinger	Yes	No	Yes	No

As nouns, precursor and harbinger are synonyms defined as:

precursor and harbinger: something that precedes and indicates the approach of something or someone

Other synonyms of precursor include forerunner, herald, predecessor.

precursor (noun)	harbinger (noun)
something that precedes and indicates the approach of something or someone	something that precedes and indicates the approach of something or someone
a person who goes before or announces the coming of another
a substance from which another substance is formed (especially by a metabolic reaction)

precursor (verb)	harbinger (verb)
	foreshadow or presage