ǵʰel-
“to shine, yellow, green”shine, glow, green/yellow
Root for shining/color, yielding English gold, yellow, green, glow, glass.
Discussion
The PIE root *ǵʰel- (to shine, to be yellow or green) is the single most productive colour root in the Indo-European family, generating terms for gold, yellow, green, blue, grey, and glass across virtually every branch. Its extraordinary semantic range — from the gleam of precious metal to the colour of vegetation to the transparency of glass — reflects how PIE speakers conceptualised colour through the lens of luminosity: what matters is not the hue but the shine.
The Germanic branch alone produced: gold (OE gold, PGmc *gulþą — the shining metal), yellow (OE geolu, PGmc *gelwaz — the shining colour), glow (OE glōwan — to shine with heat), gleam, glimmer, glitter, glint, glisten, glass (OE glæs — the shining/transparent material), glee (OE glēo — shining joy, brightness of spirit), and the archaic gild (to cover with gold). The clustering of gl- words relating to light and shine in English is not coincidence: it reflects the PIE root's productivity in the Germanic branch, where the initial *ǵʰ became *g and the root vowel varied through ablaut.
Latin produced a different colour strand: helvus (honey-yellow), fel (bile — the yellow substance), and possibly flāvus (golden-yellow, blond, though some derive this from a different root). The botanical term chlorophyll (Greek khlōrós, "green/yellow-green" + phýllon, "leaf") preserves the root in its green-vegetation sense.
Greek khlōrós (χλωρός, "greenish-yellow, pale green, the colour of young vegetation") is the most important Hellenic reflex, giving English chlorine (named for its yellow-green colour), chlorophyll, and the medical term chlorosis (an anaemia that gives the skin a greenish pallor). The Homeric epithet khlōrón déos ("green/pale fear") uses the same word for the colour of terror-stricken skin.
Sanskrit hári- (yellow, golden, tawny — an epithet of Vishnu and of horses) and hiranya- (gold) preserve the Indo-Iranian reflexes. The Vedic god Hari (the golden one) and the Buddhist Amitābha (infinite light) inhabit the same semantic space of divine luminosity.
Old Irish gel (bright, white) and Welsh gell (yellow) provide Celtic attestation. Lithuanian geltonas (yellow) and Old Church Slavonic zelenŭ (green) confirm the Balto-Slavic reflexes — and demonstrate the same yellow/green ambiguity found in Greek khlōrós.
The yellow/green/gold overlap is not confusion but a fundamentally different colour taxonomy from the modern English system. PIE and its early daughters categorised by luminosity and saturation rather than by hue: *ǵʰel- covered the entire bright-warm end of the spectrum from metallic gold through straw-yellow to fresh green. The modern English separation of yellow, green, and gold into distinct categories is a relatively recent development — the PIE system was organised around light, not wavelength.
Notes
Pokorny 429-434. Extremely productive root for color terms.