It forms all or part of: alfalfa; Eohippus; equestrian; equine; equus; hippo-; hippocampus; Hippocratic; Hippocrene; hippocrepian; hippodrome; hippogriff; Hippolytus; hippopotamus; Philip; philippic; Philippines; Xanthippe.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit açva-, Avestan aspa-, Greek hippos, Latin equus, Old Irish ech, Old Church Slavonic ehu-, Old English eoh, Gothic aihwa- all meaning "horse."
"female of the horse or any other equine animal," Old English meare, also mere (Mercian), myre (West Saxon), fem. of mearh "horse," from Proto-Germanic *marhijo- "female horse" (source also of Old Saxon meriha, Old Norse merr, Old Frisian merrie, Dutch merrie, Old High German meriha, German Mähre "mare"), said to be of Gaulish origin (compare Irish and Gaelic marc, Welsh march, Breton marh "horse").
The fem. form is not recorded in Gothic, and there are no known cognates beyond Germanic and Celtic, so perhaps it is a word from a substrate language. The masc. forms have disappeared in English and German except as disguised in marshal (n.). In 14c. also "a bad woman, a slut," and, apparently, also "a rabbit." As the name of a throw in wrestling, it is attested from c. 1600. Mare's nest "illusory discovery, something of apparent importance causing excitement but which turns out to be a delusion or a hoax" is from 1610s.
rodent noted for its stout, clumsy body and the defensive spines or quills that cover the body and tail, c. 1400, porke despyne, from Old French porc-espin (early 13c., Modern French porc-épic), literally "spine hog," from Latin porcus "hog" (from PIE root *porko- "young pig") + spina "thorn, spine" (see spine). The word had many forms in Middle English and early Modern English, including portepyn (influenced by port "to carry," as though "carry-spine"), porkpen, porkenpick, porpoynt, and Shakespeare's porpentine (in "Hamlet"). The same notion forms the name in other languages (Dutch stekel-varken, German Stachelschwein).
The spines grow mostly on the rump and back of the broad flat tail ; they are quite loosely attached, and when the animal slaps with its tail (its usual mode of defense) some quills may be flirted to a distance. Something like this, no doubt, gives rise to the popular notion that the porcupine "shoots" its quills at an enemy. [Century Dictionary]
May (9 years old)—"Papa, things pertaining to a horse are equine, to cows bovine, to cats feline, to dogs canine, but to hogs, is what?"
Fay (5 years)—"Porcupine, O tourse."
[Health, August 1904]