The brown offspring, from the Saxon Dunn, brown, and the termination ing, which, among the Saxons, signified offspring, as White-ing, the fair offspring, Cuth-ing, the son of Cuth. Dunning has retained its original orthography since the days of the Saxons.

Arthur, William (1857) An Etymological Dictionary of Family and Christian Names. New York: Sheldon, Blakeman. Public Domain.

DUNNING. Dunning, proprietor of Latham, co. Chester, and ancestor of the family of Lathom, or Latham, of that place, was contemporary with the malving of Domesday Book. Whether he was a continued possessor, of the Saxon race, or a Norman grantee, is, Dr. Ormerod thinks, doubtful. His son was called Siward FitzDuuning. Miscellanea Palatina, p. GO. The contemporary lord of Kiugsley, co. Chester, also bore the personal name of Dunning, as did several other persons in Norman times.

Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.