'armagnac' originates from French, specifically the place-name 'Armagnac' in Gascony; the place-name ultimately derives from the Gallo‑Roman personal-name form 'Armaniācus' (from a personal name such as 'Armanius' or 'Armanus') combined with the Gaulish/Late Latin suffix '-ācum' meaning 'place of'.

'Armaniācus' changed into Occitan 'Armanhac' and then into French 'Armagnac', and the modern English word 'armagnac' was borrowed from French to refer to the brandy produced in that region.

Initially it meant 'the estate/place of Armanius' (a personal-name based place-name), but over time it came to denote the region and, by extension, the distilled spirit produced there (the current primary meaning).