Sanlúcar comes, like its other Andalusian namesakes, from the ár. saluq “east wind, east”, with reference in this case to the situation on the eastern bank of the Guadiana. This etym seems more likely than a possible lat. sub lucare “at the foot of the forest”, suggested by Nieto Ballester (311-312).

In any case, Sanlúcar would be a false hagionym, which the official Twitter account of the Spanish Royal Family did not escape during a visit in 2020 of the King and Queen of Spain to Sanlúcar in Cádiz.(<https://www.huffingtonpost.es/entry/criticas-a-la-casa-real-por-lo-que-se-ve-en-este-tuit-es-muy-evidente_es_5e47ac89c5b64433c616c15d>.

Cited bibliography:

Nieto Ballester, Emilio. Breve diccionario de topónimos españoles. Madrid: Alianza Editorial, 1997.