Early 19th century; earliest use found in The Times. From American Spanish porteño of or relating to the Argentinian capital city Buenos Aires (or to any of a number of other cities which have a port or which have Spanish puerto in their name), (as noun) native or inhabitant of this city from puerto + -eño, suffix forming nouns and adjectives from place names. With the application specifically to Buenos Aires compare the fuller name of the city, Ciudad de la Santísima Trinidad y Puerto de Santa María de los Buenos Aires.