Proper adjective: When describing something that is related to Great Britain, it acts as a proper adjective. For example:
* British history
* British flag
* British accent
Noun: When referring to a person or people from Great Britain, it acts as a noun. For example:
* The British are known for their tea drinking.
* Many British tourists visit the United States every year.
Therefore, the word "British" is versatile and can function as both a proper adjective and a noun.