rēgia

Meaning

1. a royal palace, castle, fortress, residence; court; kingship
2. the royal tent in a camp
3. a royal city, capital
4. a roofed colonnade, portico, hall
5. the central entrance to a theatre

Latīnē defined in Latin in our graded readers

domus rēgis

rēgia -ae (f) — in Metamorphoses I, ch. 5

Declension

Lewis & Short A Latin Dictionary, 1879

Origins

Substantive noun from rēgius (“regal, royal; a royal [thing]”) directly and via various ellipses of collocative terms with feminine nouns (e.g. domus, "house", and urbs, "city"). Compare the origin of Greek βασιλική (vasilikí, “basilica”), from the Byzantine Greek term βασιλική στοά (basilikḗ stoá, “royal building”).