Origins
The word 'horse' descends from Old English 'hors,' one of the most common nouns in the earliest English texts. It traces back through Proto-Germanic *hrussą to a Proto-Indo-European root *ḱers-, meaning 'to run.' This derivation — naming the horse by its defining quality of speed — tells us something about how the Germanic-speaking peoples conceived of the animal that was central to their warfare, transport, and mythology.
The deeper linguistic story is one of replacement. Proto-Indo-European had a well-established word for the horse: *h₁éḱwos. This root is spectacularly well attested across the daughter languages. Latin 'equus,' Greek 'híppos' (from earlier *híkkwos), Sanskrit 'áśva,' Avestan 'aspa,' Tocharian B 'yakwe,' Lithuanian 'ašvà' (mare), Old Irish 'ech,' and Mycenaean Greek 'i-qo' all descend from it. In English, it survives only in learned borrowings like 'equine' and 'equestrian,' and in the obsolete Old English poetic word 'eoh,' which appears in a few early texts and in the name of the rune ᛖ.
The Germanic languages are notable for having almost entirely abandoned *h₁éḱwos in everyday speech, replacing it with *hrussą. This is not an isolated phenomenon. Several culturally significant animals underwent similar lexical replacement in Germanic: the bear (*h₂ŕ̥tḱos, preserved in Latin 'ursus' and Greek 'árktos') was replaced by *berô, 'the brown one,' presumably to avoid speaking the creature's true name — a taboo practice well documented in northern cultures. Some scholars have proposed that *hrussą similarly represents a taboo replacement, reflecting the sacred status of horses in Germanic religion and society.
Proto-Indo-European Roots
The Proto-Germanic form *hrussą is reconstructed from Old English 'hors,' Old Norse 'hross,' Old High German 'hros' or 'ros,' Old Frisian 'hros,' and Old Saxon 'hros.' The initial *hr- cluster simplified differently in different descendants: English lost the 'r' early (giving 'hors'), while German lost the 'h' (giving 'Ross,' still used in elevated or poetic German and in compounds like 'Rosskastanie,' horse chestnut). The Old Norse form 'hross' preserves the full cluster and was borrowed into Scottish and northern English dialects.
The connection of *hrussą to PIE *ḱers- ('to run') links the horse etymologically to Latin 'currere' ('to run,' source of English 'current,' 'course,' 'occur'), though the Latin words derive from a zero-grade form of the same root. If this etymology is correct, calling a horse a 'horse' is etymologically equivalent to calling it a 'runner' — a metonymic naming strategy that captures the animal's most striking characteristic.
In Old English, 'hors' was the general term, but the language also possessed a rich vocabulary of equine terminology reflecting the horse's importance in Anglo-Saxon society. 'Mearh' (cognate with Irish 'marc') meant a riding horse or steed; 'wicg' was a poetic word for horse; 'hengest' meant a stallion (famously borne as a personal name by the legendary Saxon leader); and 'mȳre' (modern 'mare') designated a female horse.
Middle English
The Middle English period saw 'horse' consolidate its position as the dominant general term. The Old French 'cheval' (from Latin 'caballus,' itself a word of uncertain, possibly Celtic origin) entered English in specialized compounds like 'chivalry' and 'cavalry' but never challenged 'horse' as the basic word. This resistance to French replacement is notable given that much of English animal vocabulary was supplemented or displaced by French terms after the Norman Conquest — we eat 'beef' (French) but raise 'cows' (English), eat 'pork' but raise 'pigs.' The horse, however, kept its English name in all registers.
The cultural weight of the horse in the Germanic world can hardly be overstated. Tacitus records that the Germanic peoples kept sacred white horses whose neighing was interpreted as prophecy. Horses were buried with their riders in Anglo-Saxon graves. The legendary founders of Kent, Hengist and Horsa, both bear horse-related names (Horsa being directly related to 'horse'). The White Horse of Uffington, carved into a Berkshire hillside perhaps 3,000 years ago, still gallops across the chalk.
The word 'horse' thus carries in its etymology a double displacement: the original Indo-European name was discarded, possibly out of taboo reverence, and replaced by a Germanic word celebrating the animal's speed — a quality that made the horse, for thousands of years, the most transformative animal in human civilization.