What does Santiago mean?
A contraction of 'Sant Yago' — Saint James. Yago (also Iago) is the old Spanish form of Jacobo/James, from the Hebrew Ya'aqov (Jacob). The name honors Santiago the Apostle, patron saint of Spain, whose shrine is at Santiago de Compostela.
What does Thiago mean?
A form of Tiago, drawn from Santiago ('Sant Iago', Saint James) by resegmenting San-Tiago. The 'Th' spelling is Portuguese-influenced and hugely popular across Latin America. Ultimately traces to the Hebrew Ya'aqov (Jacob), via James.