'Forfarshire' originates from English, formed by the place-name 'Forfar' combined with the Old English word 'shire', where 'shire' meant 'administrative district' or 'county'.

'Forfarshire' derived from earlier usages such as 'Shire of Forfar' and was the conventional county name; over time the name 'Angus' came into wider common use for the same area, making 'Forfarshire' chiefly a historical name.

Initially, it meant 'the shire (county) of Forfar'; over time it has become largely a historical or archaic name for the area now usually called 'Angus'.