The name Bretel is of uncertain derivation. However, given the occurrence of the forms Britail and Brytthael in the pre-Conquest Bodmin manumission records, a masculine Old Cornish name seems a more likely solution than von Feilitzen (1937: 208) allowed for the TRE form, with the TRW forms probably representing the Old Breton equivalent.
von Feilitzen 1937: O. von Feilitzen, The Pre-Conquest Personal Names of Domesday Book, Nomina Germanica 3 (Uppsala, 1937)
Spelling in Domesday Book: Bretel
Spelling in Exon DB: Bret(t)ellus
Forms in modern scholarship:
von Feilitzen head forms: Bretel
Phillimore edition: Bretel
Alecto edition: Bretel