authoritative

adjective

1. 1

   Arising or originating from a figure of authority

   “The authoritative rules in this school come not from the headmaster but from the aged matron.”

2. 2

   Highly accurate or definitive; treated or worthy of treatment as a scholarly authority

   “This book is the world's most authoritative guide to insect breeding habits.”

3. 3

   Having a commanding style.

   “He instructed us in that booming, authoritative voice of his.”