Briton

Concise Oxford English Dictionary © 2008 Oxford University Press:
Briton/ˈbrɪtn/

▶noun

• 1 a native or inhabitant of Great Britain, or a person of British descent.

• 2 a Celtic inhabitant of southern Britain before and during Roman times.

– origin from OFr. Breton, from L. Britto, Britton-, or its Celtic equivalent.