salvo vs flare-up

salvo and flare-up both are nouns.

Word	Noun	Adjective	Verb	Adverb
salvo	Yes	No	No	No
flare-up	Yes	No	No	No

As nouns, flare-up is a hypernym of salvo; that is, flare-up is a word with a broader meaning than salvo:

salvo: an outburst resembling the discharge of firearms or the release of bombs
flare-up: a sudden intense happening

Other hypernyms of salvo include burst, outburst.

salvo (noun)	flare-up (noun)
rapid simultaneous discharge of firearms	a sudden intense happening
a sudden outburst of cheers
an outburst resembling the discharge of firearms or the release of bombs