Imperious, a.
Etymology: [L. imperiosus: cf. F. impérieux. See Imperial.]
1. Commanding; ascendant; imperial; lordly; majestic. [Obs.] "A vast and imperious mind." Tilloison. Therefore, great lords, be, as your titles witness, Imperious. Shak.
2. Haughly; arrogant; overbearing; as, an imperious tyrant; an imperious manner. This imperious man will work us all From princes into pages. Shak. His bold, contemptuous, and imperious spirit soon made him conspicuous. Macaulay.
3. Imperative; urgent; compelling. Imperious need, which can not be withstood. Dryden.
Syn. -- Dictatorial; haughty; domineering; overbearing; lordly; tyrannical; despotic; arrogant; imperative; authoritative; commanding; pressing. -- Imperious, Lordly, Domineering. One who is imperious exercises his authority in a manner highly offensive for its spirit and tone; one who is lordly assumes a lofty air in order to display his importance; one who is domineering gives orders in a way to make other feel their inferiority.
Shades of meaning
Fernald has no entry of its own for imperious; he lists it under absolute, dogmatic.
Where he writes about it:
Authoritative is used always in a good sense, implying the right to claim authority; imperative, peremptory, and positive are used ordinarily in the good sense; as, an authoritative definition; an imperative demand; a peremptory command; positive instructions; imperious signifies assuming and determined to command, rigorously requiring obedience. — from absolute
An imperious demand or requirement may have in it nothing offensive; it is simply one that resolutely insists upon compliance, and will not brook refusal; an arrogant demand is offensive by its tone of superiority, an arbitrary demand by its unreasonableness; an imperious disposition is liable to become arbitrary and arrogant. — from absolute
A person of an independent spirit is inclined to resent an imperious manner in any one, especially in one whose superiority is not clearly recognized. — from absolute