Uno, with one U, and as far as I know there are no natively Spanish words with a double U, means one. It can be used for the indefinite third person. English can use "one" for it but usually other constructions are used, such as "you" and even "we". Although it is the number one, it is more comparable to French indefinite third person "on". Advocates of inclusive language generally change the -o ending as usual though.