breakup vs severance

breakup and severance both are nouns.

Word	Noun	Adjective	Verb	Adverb
breakup	Yes	No	No	No
severance	Yes	No	No	No

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

Other hyponyms of breakup include breach, break, falling out, rift, rupture, break.

breakup (noun)	severance (noun)
the termination or disintegration of a relationship (between persons or nations)	the act of severing
coming apart	a personal or social separation (as between opposing factions)