Where did swansea get its name?

Swansea's name may be derived from Sveinn's island - the reference to an island may refer to a bank at the mouth of the river Tawe, or an area of raised ground in marshes. An alternative explanation is that the name derives from the Norse name 'Sweyn' and 'ey', which can mean inlet. The name is pronounced Swans-y, not Swan-sea.