separation vs disunion

separation and disunion both are nouns.

Word	Noun	Adjective	Verb	Adverb
separation	Yes	No	No	No
disunion	Yes	No	No	No

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

separation (noun)	disunion (noun)
the social act of separating or parting company	the termination or destruction of union
the act of dividing or disconnecting
(law) the cessation of cohabitation of man and wife (either by mutual agreement or under a court order)
sorting one thing from others
the distance between things
coming apart
the termination of employment (by resignation or dismissal)
the space where a division or parting occurs
the state of lacking unity