From Late Latin Andreati (attested in Dalmatia, 6th century, CIL III 9561), late genitive form of Andreas (“Andrew”), from Ancient Greek Ἀνδρέᾱς (Andréās); so meaning "Andrew's" (place/villa/property).
During the Late Middle Ages this became the surname of a powerful noble family from Northern Galicia, later passing into Portugal, Spain, the rest of Europe, the New World and the Philippines.