Late 18th century; earliest use found in Menon's French Family Cook. From French portugaise (early 17th century or earlier in à la portugaise prepared in Portuguese style, applied to various savoury or sweet dishes, e.g. oeufs à la Portugaise, ragout à la portugaise, omelette à la Portugaise, pomme à la portugaise; 1890 as noun in sense ‘Portuguese oyster’), feminine of portugais.