Regal comes from Latin 'rēgālis' (royal), from 'rēx' (king), and is a more Latinate doublet of 'royal,' sharing the PIE root *h₃reǵ- (to rule).
Of, resembling, or fit for a monarch, especially in being magnificent or dignified; royal.
From Old French 'regal' (royal, kingly), from Latin 'rēgālis' (of or belonging to a king, royal), from 'rēx' (genitive 'rēgis,' king), from 'regere' (to rule, to direct, to keep straight), from Proto-Indo-European *h₃reǵ- (to straighten, to direct). The word is a doublet of 'royal' — both derive from Latin 'rēgālis,' but 'regal' came directly while 'royal' came through Old French 'roial/real,' which had altered the Latin form more significantly. Key roots: rēx (rēgis) (Latin: "king"), *h₃reǵ- (Proto-Indo-European: "to straighten, to direct, to rule