kerh₂-

Root for horn/head, yielding Latin cornū and English horn, unicorn, cerebral, rhinoceros.‍​‌​‍​‍​‌​‍​‌​‍​‌​‍​‍​‍​‍​‌​‍​‌​‌​‌​‌​‍​‌​‍​‍​‍​‌​‍​‌​‍​‌​‍​‍​‍

Discussion

The Proto-Indo-European root *kerh₂- meant "horn, head, top" and is one of the most prolific roots in the reconstructed lexicon, generating a vast network of words across all major branches.‍​‌​‍​‍​‌​‍​‌​‍​‌​‍​‍​‍​‍​‌​‍​‌​‌​‌​‌​‍​‌​‍​‍​‍​‌​‍​‌​‍​‌​‍​‍​‍ The laryngeal *h₂ affected the vowel colouring and contributed to the long vowels seen in certain derivatives. The root's semantic range — from the literal horn of an animal to anything projecting, peaked, or head-like — made it extraordinarily fertile.

In Germanic, the root produced Old English horn, which has remained virtually unchanged for over a thousand years. By Grimm's Law, the Proto-Indo-European *k became Germanic *h, visible in words like hart (a male deer, named for its horns) and perhaps harvest (the "top" or culmination of the growing season, though this etymology is debated). The word horn itself is used both literally and metaphorically — a musical horn, the horn of a dilemma, Cape Horn.

Latin cornu "horn" is the most productive reflex for English vocabulary: corner (a projecting angle), cornet (a small horn), cornucopia ("horn of plenty"), unicorn ("one-horn"), Capricorn (the "horned goat" constellation), and cornea (the horn-like transparent layer of the eye). The word cerebral derives from a related Latin form cerebrum "brain", literally "the thing in the head".

Greek keras "horn" gave English rhinoceros (literally "nose-horn"), keratin (the protein of horns, hair, and nails), and triceratops ("three-horned face"). Sanskrit śṛṅgam "horn" is a further cognate showing the expected satem reflex of the initial velar.

The root also produced words for "head" and "top" in various branches, as the horn was conceptually linked to the highest point of an animal. The semantic chain from horn to head to summit to corner demonstrates the Proto-Indo-European tendency to derive abstract spatial concepts from concrete animal anatomy.