onset vs penetration

onset and penetration both are nouns.

Word	Noun	Adjective	Verb	Adverb
onset	Yes	No	No	No
penetration	Yes	No	No	No

As nouns, penetration is a hyponym of onset; that is, penetration is a word with a more specific, narrower meaning than onset:

onset (noun)	penetration (noun)
(military) an offensive against an enemy (using weapons)	an attack that penetrates into enemy territory
the beginning or early stages	the act of entering into or through something
	the act (by a man) of inserting his penis into the vagina of a woman
	the depth to which something penetrates (especially the depth reached by a projectile that hits a target)
	the ability to make way into or through something
	clear or deep perception of a situation