Possibly means
"white ring", derived from Welsh
gwen meaning "white, blessed" and
dolen meaning "ring, loop". This name appears in Geoffrey of Monmouth's 12th-century chronicles, written in the Latin form
Guendoloena, where it belongs to an ancient queen of the Britons who defeats her ex-husband in battle
[1]. Geoffrey later used it in
Vita Merlini for the wife of the prophet
Merlin [2]. An alternate theory claims that the name arose from a misreading of the masculine name
Guendoleu by Geoffrey
[3].
This name was not regularly given to people until the 19th century [4][3]. It was used by George Eliot for a character in her novel Daniel Deronda (1876).