h₁regʷ-

The root *h₁regʷ- is less widely attested than many PIE reconstructions and carries a correspondingly lower confidence level, though the available cognates are phonologically regular and semantically coherent. Greek Érebos (Ἔρεβος, "darkness, the dark underworld") is the most culturally prominent reflex. In Hesiod's Theogony, Erebos is a primordial deity born from Chaos, representing the darkness of the underworld in contrast to Nyx (Night), the darkness of the surface world. The distinction between subterranean and atmospheric darkness may reflect an inherited cosmological schema. Sanskrit rájas ("darkness, atmosphere, dust, cosmic space") shows a broader semantic range. In Vedic cosmology, rajas denotes the atmospheric space between earth and sky — a domain characterised by its obscurity relative to the bright sky (svar) and the solid earth (bhūmi). The later philosophical use of rajas as one of the three guṇas ("qualities") in Sāṃkhya philosophy — representing passion, activity, and turbulence — develops from the atmospheric sense. Gothic riqis ("darkness") and Old Norse røkkr ("darkness, twilight" — as in Ragnarøkkr, one variant of the name for the Norse apocalypse) continue the Germanic reflex with regular phonological development. Armenian erek ("evening") has been connected, though the phonological details are debated. The pairing of *h₁regʷ- ("darkness") with *lewk- ("light") and *h₂ews- ("dawn") suggests that PIE possessed a structured vocabulary for the divisions of the day and the contrasts of the sky. The cosmological significance of this vocabulary — encoded in mythology from Greece to India — points to an inherited framework for conceptualising the natural world.