Regius | Webster's Dictionary of the English Language

regius
rēgĭus, a, um, adj. [rex], of or belonging to a king, kingly, royal, regal. I Lit.: cum esset haben...

A New Latin Dictionary by Charlton T. Lewis Ph.D. and Charles Short, LL. D.
regius
rēgius adj. rex, of a king, kingly, royal, regal : genere regio natus: potestas: appara...

An Elementary Latin Dictionary