ground attack vs onset

ground attack and onset both are nouns.

Word	Noun	Adjective	Verb	Adverb
ground attack	Yes	No	No	No
onset	Yes	No	No	No

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

Other hypernyms of ground attack include attack, onrush, onslaught.

ground attack (noun)	onset (noun)
an attack by ground troops	(military) an offensive against an enemy (using weapons)
	the beginning or early stages