authority vs mandator

authority and mandator both are nouns.

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

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

authority: (usually plural) persons who exercise (administrative) control over others
mandator: an authority who issues a mandate

authority (noun)	mandator (noun)
the power or right to give orders or make decisions	an authority who issues a mandate
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