Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
BILLY
As described in historical dictionaries
Patronymica Britannica (1860)
BILLY. N'otfrom'\Yilliam,butfrom aplace in thearroudissementof Caen, inNormandj'. Also a comrade, compaiuon. Jamiesou.