'auctor' originates from Latin, specifically the word 'auctor', which derives from the verb 'augēre' (classical form 'augēre'), where the root 'aug-' meant 'to increase' or 'to promote'.

'auctor' in Latin passed into Medieval Latin and Old French forms such as 'auctour'/'aucteur', then into Middle English (spelled 'auctor' or 'author'), eventually yielding the modern English word 'author' while the original Latin form survives in scholarly or legal usages.

Initially it meant 'one who increases or promotes' (in the sense of giving growth or authority), and over time it narrowed to the current primary sense 'author' or 'originator' of a work; additionally it acquired the specialized sense 'guarantor' or 'source of authority' in legal/ecclesiastical contexts.