authoritāˈrian adjective

1. Setting authority above freedom
2. Relating to, governed by, or stressing the importance and power of authority, or of a small group representing it
3. Domineering, disciplinarian

An authoritarian person

authoritāˈrianism noun

authoritative /ö-thorˈit-āt-iv or ö-thorˈit-ət-iv/ adjective

1. Having the sanction or weight of authority
2. Accepted, approved
3. Definitive, reliable
4. Dictatorial

authorˈitatively adverb

authorˈitativeness noun

have on good authority

To be confident of the truth of a statement