Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
GUN
As described in historical dictionaries
Patronymica Britannica (1860)
GUNN. GUN. An ancient personal name, or rather a contraction of one, such as Gundebert, Gundric, or Guudbald.