Authoritative

Au*thor"i*ta*tive (?), a. 1. Having, or proceeding from, due authority; entitled to obedience, credit, or acceptance; determinate; commanding.

The sacred functions of authoritative teaching.
Barrow.

2. Having an air of authority; positive; dictatorial; peremptory; as, an authoritative tone.

The mock authoritative manner of the one, and the insipid mirth of the other.
Swift.

-- Au*thor"i*ta*tive*ly, adv. -- Au*thor"i*ta*tive*ness, n.