From a Greek name meaning ‘life’. This was already in use in Rome towards the end of the classical period (at first as an affectionate nickname), and was popular with the early Christians, who bestowed it with reference to their hopes of eternal life. It was borne by martyrs of the 2nd and 3rd centuries, but was taken up as an English given name only in the 19th century. It has been consistently popular in Britain since the 1970s.
Spanish, Catalan, and Jewish (Sephardic): habitational name from any of numerous places called Aguilar, from Latin aquilare ‘haunt of eagles’ (a derivative of aquila ‘eagle’), for example Aguilar de Campo in Palencia, Aguilar de la Frontera in Córdoba, and Aguilar de Segarra in Catalonia.