banzai attack vs onset

banzai attack and onset both are nouns.

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

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

banzai attack: a mass attack of troops without concern for casualties; originated by Japanese who accompanied it with yells of `banzai'
onset: (military) an offensive against an enemy (using weapons)

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

banzai attack (noun)	onset (noun)
a mass attack of troops without concern for casualties; originated by Japanese who accompanied it with yells of `banzai'	(military) an offensive against an enemy (using weapons)
	the beginning or early stages