au·thor·i·ta·tive 
/əˈθorəˌteɪtɪv/ adjective
/əˈθorəˌteɪtɪv/ adjective [more authoritative; most authoritative] 1 : having or showing impressive knowledge about a subject
▪ He is an authoritative [=reliable, accurate] source for information about Islamic art. ▪ The book is an authoritative guide to the city's restaurants. 2 : having the confident quality of someone who is respected or obeyed by other people
▪ His manner is polite but authoritative. ▪ She addressed the group with an authoritative voice.
▪ He is an authoritative [=reliable, accurate] source for information about Islamic art. ▪ The book is an authoritative guide to the city's restaurants.
▪ His manner is polite but authoritative. ▪ She addressed the group with an authoritative voice.
— au·thor·i·ta·tive·ly adverb
▪ She spoke authoritatively [=with authority] about the history of the building.
▪ She spoke authoritatively [=with authority] about the history of the building.
