dyew-
“to shine (as divine sky), divine”divine/sky-god
PIE root meaning to shine as the divine sky. Source of Latin Iuppiter, Sanskrit Dyaus, and words for deity and daylight.
Discussion
The root *dyew- ("to shine, sky, heavenly light") is the source of the PIE sky-god name *Dyḗws ph₂tḗr ("Sky Father"), one of the most celebrated reconstructions in comparative linguistics. Pokorny (IEW 183–187) and LIV² treat this as a primary root meaning "to be bright, to shine as daylight." The full grade *dyew- and the zero grade *diw- alternate in nominal and verbal formations.
Sanskrit Dyáuṣ pitā́ ("Sky Father") directly continues the PIE divine name, with dyáuṣ ("sky, heaven, day") as the nominative. The accusative divám and genitive diváḥ show the zero-grade *diw-. Greek Zeús (Ζεύς), genitive Diós (Διός), continues the same divine name; the vocative Zeû reflects *dyew with regular Greek sound changes. The derivative *diw-os gives Latin dīvus ("divine") and deus ("god"), from earlier deivos, whence English divine, deity, and deify. Latin diēs ("day") reflects the nominal stem *dyew- directly, giving English diurnal, diary, and journal (via Old French, from Latin diurnālis).
In Germanic, the zero grade *tīw- (with regular *d > t by Grimm's Law) produces Old English Tīw, the war-god whose name survives in Tuesday. Old Norse Týr preserves the same theonym. Gothic lacks a direct divine reflex but has the adjective *tīwiska- implied by Old High German ziostag.
The root shows no laryngeal (*dyew- not **dHyew-), and the ablaut alternation *dyew-/*diw- is canonical. The semantic development from "bright sky" to "god" to "day" is paralleled independently in multiple branches, making *dyew- a cornerstone of PIE cultural and religious vocabulary.
Notes
Source of Latin "deus", "dīvīnus", Sanskrit "devá". The celestial divinity root.