Erwan Vallerie ː Treguenc, XIvet; Treguent, 1038; Treguenc, 1084; Treguent, XIIvet; Treguenc, 1112; Tregunc, 1270; Trefguen, 1368; Trefguenc, 1368; Tresguenc, 1368; Tregueuc, 1370; Treguenc, 1516, 1536; Treguen, 1630