Use 'authoritative' when referring to people or texts respected for their deep knowledge. She is an authoritative figure in child psychology.
Pro Tip 2/3
Not Always Right
'Authoritative' doesn't mean infallible; even reliable sources can be questioned. Despite the study's authoritative reputation, its findings were later challenged.
Pro Tip 3/3
Subject-Specific
An 'authoritative' source is especially knowledgeable in a particular subject or field. The book is considered an authoritative work on European history.