porcupine n.

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]