Authoritative

Adjective

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. 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. Having a commanding style.

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