Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
FAUNTLEROY
As described in historical dictionaries
Patronymica Britannica (1860)
FAUNTLEROY. FANTLEROY. As several anrugerous families — apparently unconnected with each otlier — have borne this name, it is presumed to be of considerable antiquity in England. It is perhaps a corruption of an ancient Fr. war-cry — DEFENDEZ LE ROI — ' Defend the King !' In course of time, the meaning of the name being forgotten, the De would be dropped, and the remaining syllables would easity glide into Fauntleroy. For examples of other surnames derived from war-cries, see Hay and Halliday.