proscription vs fiat

proscription and fiat both are nouns.

Word	Noun	Adjective	Verb	Adverb
proscription	Yes	No	No	No
fiat	Yes	No	No	No

As nouns, fiat is a hypernym of proscription; that is, fiat is a word with a broader meaning than proscription:

proscription: a decree that prohibits something
fiat: a legally binding command or decision entered on the court record (as if issued by a court or judge)

Other hypernyms of proscription include decree, edict, order, rescript.

proscription (noun)	fiat (noun)
rejection by means of an act of banishing or proscribing someone	a legally binding command or decision entered on the court record (as if issued by a court or judge)
a decree that prohibits something