h₃reǵ-s-
“king, ruler”Source of Latin rēx, English regal, reign, royal, regicide
Extended form for ruler, yielding Latin rēx (king) and English regal, reign, royal, regicide.
Discussion
The PIE form *h₃reǵ-s (king, ruler) is an agent noun from *h₃reǵ- (to move in a straight line, to direct, to rule), meaning literally "the one who directs" — the king as the keeper of the straight path.
Latin rēx (king — genitive rēgis) is the direct continuation: regal, regent, regime, regicide (killing of a king), and the personal name Rex. The Celtic cognate appears in the Gaulish tribal title -rīx (Vercingetorix, "great king of warriors") and Old Irish rí (king). Sanskrit rā́jan- (king, ruler) continues the Indo-Iranian reflex — Maharaja means "great king."
The word's significance extends beyond political vocabulary. The connection between *h₃reǵ- (straightening/directing) and kingship encodes a PIE political philosophy: legitimate authority IS the maintenance of straightness. The king is not the strongest or the richest but the one who keeps things on the correct path. This concept connects to *h₃reǵ-tó- (made straight → right, correct) — the moral and legal vocabulary built on the same root.
Compare *dem-s-pot- (master of the house — see *dem- for the domestic authority root) and *weyḱ- (settlement/village — see the social organisation root). PIE had multiple vocabulary items for different types of authority: the king (*h₃reǵ-s) directed the community, the household master (*dem-s-pot-) governed the home.