'Britannic' originates from Latin, specifically the word 'Britannicus', where 'Britannia' meant 'Britain'.

'Britannicus' was used in Latin to form adjectives meaning 'of Britain'; it passed into Medieval and Modern European usage and was adopted into English in the modern form 'Britannic'.

Initially it meant 'of or pertaining to (Roman) Britannia', but over time it evolved into the broader modern sense of 'relating to Britain or the British monarchy'.