Centaurii is the plural noun used to describe two or more of the races that make their home in the Alpha Centauri system. It is also the name of their common language.
The term applies generally to the the Centaurans from Alpha Centauri IV (Centaurus), the Centaurians from Alpha Centauri VII (Al Rigil), and/or the Terran colonists from Alpha Centauri II. The term is rarely, if ever, used to describe the inhabitants of the worlds orbiting Proxima Centauri. (Star Trek: Pendragon)