Sid is a diminutive of Sidney, itself a variant of Sydney. Sydney originates in Old English language and means "from a large island". It was derived from an old surname and as a surname it functions until today. This particular spelling coincides with the name of the most populous city in Australia and the state capital of New South Wales. As a given name Sydney has been used since the 19th century. It can be used as both feminine and masculine names, but currently is much more popular for girls in the United States.