IPA: /əˈθɔːrɪteɪtɪv/
KK: /əˈθɔrɪˌteɪtɪv/
Having official power or influence; recognized as reliable and accurate.
The professor provided an authoritative explanation of the complex theory.
Authoritative → It is formed from "author" (from Latin "auctor", meaning creator or originator) and the suffix "-itative" (from Latin "-ativus", meaning having the quality of). The word "authoritative" means having the quality of being a creator or originator, thus implying a commanding or influential presence.
Think of an 'author' as someone who creates or originates ideas, and remember that 'authoritative' describes someone who has the quality of being a commanding figure.