*Dyēus

*Dyḗus (lit. 'daylight'), also *Dyḗus ph₂tḗr (lit. 'father daylight'), is the reconstructed name of the daylight-sky god in Proto-Indo-European mythology. *Dyēus was conceived as a divine personification of the bright sky of the day and the seat of the gods, the *deywṓs. Associated with the vast diurnal sky and with the fertile rains, *Dyēus was often paired with *Dʰéǵʰōm, the Earth Mother, in a relationship of union and contrast.

While its existence is not directly attested by archaeological or written materials, *Dyēus is considered by scholars the most securely reconstructed deity of the Indo-European pantheon, as identical formulas referring to him can be found among the subsequent Indo-European languages and myths of the Vedic Indo-Aryans, Latins, Greeks, Phrygians, Messapians, Thracians, Illyrians, Albanians and Hittites.

The divine name *Dyēus derives from the stem *dyeu-, denoting the "diurnal sky" or the "brightness of the day" (in contrast to the darkness of the night), an expanded form of the root *di or dey- ("to shine, be bright"). Cognates in Indo-European languages revolving around the concepts of "day", "sky" and "deity" and sharing the root *dyeu- as an etymon, such as Sanskrit dyumán- 'heavenly, shining, radiant', suggest that Dyēus referred to the vast and bright sky of the day conceived as a divine entity among Proto-Indo-European speakers.

A vṛddhi-derivative appears in *deywós ("celestial"), the common word for "god" in Proto-Indo-European. In classic Indo-European, associated with the late Khvalynsk culture (3900–3500), *Dyēus also had the meaning of "Heaven", whereas it denoted "god" in general (or the Sun-god in particular) in the Anatolian tradition. The suffix-derivative *diwyós ("divine") is also attested in Latin, Greek and Sanskrit. The noun *deynos ("day"), interpreted as a back-formation of *deywós, has descendant cognates in Albanian din ("break of the day"), Vedic Sanskrit dína- "day" and divé-dive ("day by day"), Lithuanian dienà and Latvian dìena ("day"), Slavic dъnъ ("day") or Slavic Poludnitsa ("Lady Midday"), Latin Dies, goddess of the day and counterpart to Greek Hemera, Hittite siwat ("day"), Palaic Tīyat- ("Sun, day"), Ancient Greek endios ("midday"), Old Armenian tiw (տիւ, "bright day"), Old Irish noenden ("nine-day period"), Welsh heddyw ("today").

While the Greek goddess Pandeia or Pandia (Ancient Greek: Πανδία, Πανδεία, "all brightness") may have been another name for the Moon Goddess Selene, her name still preserves the root *di-/*dei-, meaning "to shine, be bright".

The most constant epithet associated with *Dyēus is "father" (*ph₂tḗr). The term "Father Dyēus" was inherited in the Vedic Dyáuṣ Pitṛ́, Greek Zeus Patēr, Illyrian Dei-pátrous, Roman Jupiter (*Djous patēr), even in the form of "dad" or "papa" in the Scythian Papaios for Zeus, or the Palaic expression Tiyaz papaz. The epithet *Ph₂tḗr Ǵenh₁-tōr ("Father Procreator") is also attested in the Vedic, Iranian, Greek, and perhaps the Roman ritual traditions.

*Dyēus was the Sky or Day conceived as a divine entity, and thus the dwelling of the gods, the Heaven. As the gateway to the deities and the father of both the Divine Twins and the goddess of the Dawn (*H₂éwsōs), *Dyēus was a prominent deity in the Proto-Indo-European pantheon. He was however likely not their ruler or the holder of the supreme power like Zeus and Jupiter.

*Dyēus was associated with the bright and vast sky, but also to the cloudy weather in the Vedic and Greek formulas *Dyēus' rain. Although several reflexes of Dyēus are storm deities, such as Zeus and Jupiter, this is thought to be a late development exclusive to Mediterranean traditions, probably derived from syncretism with Canaanite deities and the Proto-Indo-European god *Perkʷūnos.