1. The highest rated or regarded; the best. Spanish for "number one." It can be used as a noun or an adjective. If you're looking for a good burger, this place is numero uno. Happy birthday to my numero uno friend!

2. noun Oneself. In this usage, the term implies that one's top priority or concern is or should be oneself. Used especially with the phrase "look out for numero uno." You need to be careful in situations where there's a stampede toward an exit, because everybody is just looking out for number uno.