1701, "pertaining to a dictator; absolute, unlimited;" see dictator + -ial. Meaning "imperious, overbearing" is from 1704. Related: Dictatorially. Earlier in the sense "pertaining to a dictator" were dictatorian (1640s); dictator-like (1580s). "Dictatorial implies, on the one hand, a disposition to rule, and, on the other, a sharp insistence upon having one's orders accepted or carried out." [Century Dictionary]
