Elvet, the place, means "swan", so it's redundant. the word is recorded as ilfette, aelbitu, Ilfatu, Ilfetu, Ylfete, Elfetu, and ylfette. there are other Germanic cognates of similar form, which for obvious reasons are suggested to be related to alb- 'white', but which are probably a variant of the root of auk and latin olor 'swan'.