au·thor·i·ta·tive 
(ə-thôrĭ-tā′tĭv, ə-thŏr-, ô-)
(ə-thôrĭ-tā′tĭv, ə-thŏr-, ô-)adj.
1. Having or arising from authority; official: an authoritative decree; authoritative sources.
2. Of acknowledged accuracy or excellence; highly reliable: an authoritative account of the revolution.
3. Demonstrating authority; commanding: the captain's authoritative manner.
au·thori·ta′tive·ly adv.
au·thori·ta′tive·ness n.