It seems to have an anthroponymic origin, as is presumed in the western Galician area for Rubiáns, from a Latin name Rubianus. This origin is also adduced for Rubiá (villa Rubiana, from a possible Rubius), as Domínguez Quiroga points out (252).

Cited bibliography: 

-Domínguez Quiroga, Manuel. Toponimia da provincia de Ourense. Ourense: Deputación Provincial de Ourense, 2017.