Why is it called a 'Quid'?

The term 'quid' for a British pound has been used for centuries, but its origins remain somewhat mysterious.

The most widely accepted theory suggests it comes from the Latin phrase 'quid pro quo,' meaning 'something for something.'

Another theory proposes that 'quid' derives from Quidhampton, though this is less commonly supported.

Whatever the origin, 'quid' has remained one of the most stable slang terms in British English.