phrase/a ˈuɾto/
stealthily, in secret
“Andava don Francisco transformado en su amor y convertido en sombra de su dama, sin perderla de vista, dando los mismos bordos y passeos y valiéndose de ocasiones que, a hurto, dieron lugar de hablarse, y aun tocarse las manos, favor que enloquezía a mi cautivo amigo, no sin gran risa mía” — Don Francisco was now going about transformed in love, converted into his lady's shadow not losing sight of her, taking walks in the places and making the most out of times when, in secret, they were able to speak and even join hands, which made my enthralled friend crazy, not without my laughter
Inherited from Old Spanish a furto, inherited from Latin fūrtō (“stealthily”) with preposition reinforcing. Compare Romanian (pe) furiș