imperium vs authority

imperium and authority both are nouns.

Word	Noun	Adjective	Verb	Adverb
imperium	Yes	No	No	No
authority	Yes	No	No	No

As nouns, authority is a hypernym of imperium; that is, authority is a word with a broader meaning than imperium:

Other hypernyms of imperium include authorisation, authorization, dominance, potency, say-so.

imperium (noun)	authority (noun)
supreme authority; absolute dominion	the power or right to give orders or make decisions
the domain ruled by an emperor or empress; the region over which imperial dominion is exercised	official permission or approval
	freedom from doubt; belief in yourself and your abilities
	an authoritative written work
	an administrative unit of government
	an expert whose views are taken as definitive
	(usually plural) persons who exercise (administrative) control over others