Author from Latin auctor (originator, one who causes to grow), from augēre (to increase), PIE *h₂ewg-. Roman auctores were not just writers — founders, lawmakers, guarantors. Medieval scholars narrowed it to canonical writers. The -th- spelling is a Renaissance hypercorrection from false Greek association. Same root as augment, august, auction, inaugurate, auxiliary.
The writer or originator of a literary work; one who creates, initiates, or is responsible for something.
From Anglo-French autour, Old French autor, from Latin auctor (one who causes to grow, a creator, a founder, an originator, a responsible person), from augēre (to increase, to cause to grow, to make greater), from Proto-Indo-European *h₂ewg- (to increase, to enlarge, to prosper). An auctor was the one who gave increase — who caused something to come into being and gave it its force. Roman law used auctor for a guarantor or sponsor; Roman rhetoric used it for a cited authority