Autocratic, Autocratical, a.
Of or pertaining to autocracy or to an autocrat; absolute; holding independent and arbitrary powers of government. -- Au`to*crat"ic*al*ly, adv.
Shades of meaning
Fernald has no entry of its own for autocratic; he lists it under absolute.
Where he writes about it:
Autocratic power knows no limits outside the ruler's self; arbitrary power, none outside the ruler's will or judgment, arbitrary carrying the implication of wilfulness and capriciousness. — from absolute