British
Old English Brettisc ‘relating to the ancient Britons’, from Bret ‘Briton’, from Latin Britto, or its Celtic equivalent.
wiktionary
From Old English Bryttisċ(“ Britons”). [1] The spelling with single -t- appears in the 13th century under the influence of Medieval Latin Britannicus, but spelling with -tt- persists alongside -t- during the 13th to 17th centuries.
In reference to the island of Great Britain from ca. 1400 (Latin natio Anglica sive Britannica, Brittisshe occean 1398, the Britishe nacion 1548). As a noun, referring to the British people, British soldiers, etc. from ca. 1600.
etymonline
British (adj.)
Old English Bryttisc "of or relating to (ancient) Britons," from Bryttas "natives of ancient Britain" (see Briton). Meaning "of or pertaining to Great Britain" is from c. 1600; the noun meaning "inhabitants of Great Britain" is from 1640s. British Empire is from c. 1600. First modern record of British Isles is from 1620s. British English as the form of the English language spoken in Britain is by 1862 (George P. Marsh). Related: Britishness.
