Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
GIL
As described in historical dictionaries
Patronymica Britannica (1860)
E GILL. GIL. A prefix of many old Gaelic personal names now become surnames. Like the Lowland Scotch Gillie, it means a menial servant. In the early ages of Christianity in Scotland, it was ordinary for religious persons to devote and designate themselves as servants, either of the Saviour or of some saint. Hence among others the names — Gillies, the servant of Jesus.
Origin: Iberian
Region of origin: Europe
Country of origin: Spain
Religion of origin: Christian
Language of origin: Spanish