incursion vs onset

incursion and onset both are nouns.

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

As nouns, onset is a hypernym of incursion; that is, onset is a word with a broader meaning than incursion:

Other hypernyms of incursion include attack, onrush, onslaught.

incursion (noun)	onset (noun)
an attack that penetrates into enemy territory	(military) an offensive against an enemy (using weapons)
the act of entering some territory or domain (often in large numbers)	the beginning or early stages
the mistake of incurring liability or blame