h₁rewdʰ-

Root for red color.‌​‍​‍​‌​‌​‍​‍​‌​‍​‌​‌​‌​‌​‍​‍​‌​‍​‍​‌​‍​‍​‌​‍​‍​‌​‌​‍​‍​‌​‍​‌​‌ Gives Latin ruber, English "red", "rust", "ruddy", Greek eruthrós.

Discussion

The root *h₁rewdʰ- ("red, ruddy") is treated in Pokorny (IEW 872–873) and reconstructed with an init‌​‍​‍​‌​‌​‍​‍​‌​‍​‌​‌​‌​‌​‍​‍​‌​‍​‍​‌​‍​‍​‌​‍​‍​‌​‌​‍​‍​‌​‍​‌​‌ial laryngeal *h₁ based on the absence of vowel colouring and the behaviour of the vowel in Anatolian. This is the primary PIE colour term for redness.

Latin ruber ("red") and rufus ("red-haired") continue the root with regular *h₁r- > r- and *dʰ > b/f. From Latin come English rubric (originally a heading written in red ink), ruby, rubella, rubicund, and rouge (via French). Rōbīgō ("rust, red blight on wheat") may also belong here. The personal name Rufus ("the red-haired one") was common in Roman naming.

Greek eruthrós (ἐρυθρός, "red") preserves the full grade with the prothetic e- typical of Greek laryngeal reflexes. The Red Sea is Eruthḕ Thálassa in Greek, and the chemical element erbium takes its name indirectly from this family. Erythrocyte ("red blood cell") uses the Greek combining form directly.

In Germanic, Grimm's Law gives *h₁rewdʰ- > *raud-: Old English rēad ("red"), whence Modern English red. Old Norse rauðr, Old High German rōt, and Gothic rauþs are cognates. The English words ruddy, rust (the red oxide), and robin (the red-breasted bird) all derive from this root. The personal name Roderick ("famous ruler") contains an unrelated element, but Rufus and Russell come from the Latin branch of the same root.

Sanskrit rudhirá- ("red, bloody") and róhita- ("red, reddish") preserve the Indo-Iranian reflexes. Lithuanian raũdas ("red, reddish-brown") and Old Church Slavonic rudъ ("red") confirm the Baltic and Slavic branches.

The root shows standard ablaut (*h₁rewdʰ-/*h₁rowdʰ-/*h₁rudʰ-). The equation red = ruber = eruthrós = rēad is one of the foundational correspondences of comparative linguistics.

Notes

Source of "erythrocyte", "rubric", "ruby", "robust"