Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
FATT
As described in historical dictionaries
Patronymica Britannica (1860)
FATT. Stout, large as to person. So tlie Fr. Le Gros, and the Germ. Feist, both naturalized as surnames in England.