ḱerh₂-
“gray, dark color”gray, dusky
Root for gray or dark coloring. Gives English "hare" (gray animal), Latin cervus "deer" (brown one).
Discussion
The Proto-Indo-European root *ḱerh₂- meant "gray, dark, dusky" and belongs to the colour terminology of the proto-language — a domain that was considerably less elaborate than the colour systems of modern languages. The initial palatal *ḱ places this root in the group affected by the centum-satem division, and the laryngeal *h₂ influenced the vowel quality of its derivatives.
The primary English descendant is hare, from Old English hara, literally "the gray one". Naming animals by their colour is a common Indo-European practice — the bear, the beaver, and the elk all have colour-related etymologies in various branches. The hare's grayish-brown coat made this an obvious designation. The word hoar, as in hoar-frost (gray frost) and hoary (gray-haired, venerable), also descends from this root, preserving the original colour meaning more transparently.
In Germanic, the palatal *ḱ became a velar *k and then, by Grimm's Law, the fricative *h, producing the initial h- of hare and hoary. The vowel was affected by the laryngeal, producing the long ā that became the oa of hoar in modern English.
Latin cānus "gray, white-haired" is a probable cognate, though the connection is not accepted by all specialists. If correct, it would link to English canescent "becoming gray". More securely, Old High German haso "gray, dull" (the source of German Hase "hare") confirms the Germanic picture.
The root *ḱerh₂- reminds us that the Proto-Indo-European colour vocabulary was oriented towards brightness and darkness rather than the hue-based system familiar to modern speakers. "Gray" in this context likely meant something closer to "dark, dusky" — a quality of diminished light rather than a specific spectral value. Animal names built on colour terms provide valuable evidence for this early, luminosity-based approach to colour classification.
Notes
Color words often attached to animals in IE