Definition of British adjective from the Oxford Advanced Learner's Dictionary
British
adjective
ˈbrɪtɪʃ ˈbrɪtɪʃ
1(abbr.Br.) connected with the United Kingdom of Great Britain and Northern Ireland or the people who live therethe British GovernmentHe was born in France but his parents are British.British-based/British-born/British-made2the Britishnoun[plural]the people of the United KingdomBritishness
ˈbrɪtɪʃnəs ˈbrɪtɪʃnəs
noun[uncountable]
Usage note: the BritishThere is no singular noun which is commonly used to refer to a person from Britain. Instead the adjective British is used: She’s British.◇The British have a very odd sense of humour. The adjective English refers only to people from England, not the rest of the United Kingdom.The noun Briton is used mainly in newspapers: The survivors of the avalanche included 12 Britons. It also describes the early inhabitants of Britain: the ancient Britons. Brit is informal and can sound negative. Britisher is now very old-fashioned. note at Scottish
ˈbrɪtɪʃ 
ˈbrɪtɪʃ 
Usage note: the BritishThere is no singular noun which is commonly used to refer to a person from Britain. Instead the adjective British is used: She’s British. ◇ The British have a very odd sense of humour. The adjective English refers only to people from England, not the rest of the United Kingdom.The noun Briton is used mainly in newspapers: The survivors of the avalanche included 12 Britons. It also describes the early inhabitants of Britain: the ancient Britons. Brit is informal and can sound negative. Britisher is now very old-fashioned. note at Scottish