A short word with two jobs
Pelt is one of those compact English words that looks simple until you try to put it in a single dictionary box. As a noun it is the untreated skin of an animal with the hair, wool, or fur still attached, the sort of hide a trapper or a furrier would handle, and later also a skin already stripped for tanning. As a verb it is to throw things at someone in a stream, to hammer down as rain does on a roof, or to race along at full pelt. Those uses sit side by side in modern English, but they did not grow from one root. Anyone hunting a single origin of the word pelt has to be told there is no single line. What we have is a pair of homonyms that reached the language by different routes and then collapsed onto the same short spelling.
The hide
The noun is the older of the two in the written record, and even that history is not tidy. By the fifteenth century, and in some cloth-and-hide accounts a little earlier, English speakers were using pelt for the skin of a fur-bearing animal, especially the smaller creatures that supplied the fur trade. In the later sixteenth century the same noun could also mean a skin already stripped of wool or fur and waiting for the tanner. From the noun English later made a workaday verb, to pelt, meaning to strip the skin from an animal. That trade sense is recorded from the later 1500s. It is not the verb in hail pelted the roof.
Where the form itself came from is still argued. One reconstruction treats English pelt as a shortened borrowing of Anglo-French pelette or Old French pelete, a diminutive meaning a fine skin or membrane. That French word is built in a transparent way: pel, skin, plus a diminutive ending. Pel goes back to Latin pellis, hide, and that Latin noun is traced to a Proto-Indo-European root reconstructed as covering, wrapping, or skin. Another reconstruction treats pelt as a back-formation from peltry, the collective term for fur skins, itself from Anglo-French pelterie and Old French peletrie, the stock of a peletier, a furrier, again from pel. A third possibility, noted in historical dictionaries, is that English took a clipped form of post-classical Latin peletta or pelletta, words used of an animal skin, especially a sheep's.
None of these paths is proven beyond doubt. What they share is a Romance source sitting on Latin pellis, not a native Old English word of the same shape. English did keep a native cousin of that Latin noun: fell, the hide of an animal, from Old English. Film belongs to the same wider family through Old English filmen, a membrane. Those native forms make the point clearly. The everyday word for a fur skin in English was borrowed, or clipped from a borrowed cluster, while the older Germanic hide-word survived in a narrower niche.
Look-alikes in neighboring languages can mislead. German Pelz, Dutch pels, and Norwegian pels all mean fur or a fur coat and sit close to English pelt in sound. They are not evidence that English inherited pelt from Proto-Germanic. Those continental words themselves reflect Romance contact with the pellis family. Old Norse feldr, a cloak or pelt, is a better distant relative of the hide sense, sitting with fell rather than with the French diminutive.
The barrage
The striking verb is a different word. Late Middle English had pelten, a variant of pilten, to thrust or strike, and the Middle English record also shows forms such as pulten beside pelt. Dictionaries date the familiar modern sense, to hit again and again with something thrown, around 1500, with a noun for an act of pelting following in the early sixteenth century. After that the verb widened in a natural way. By the late seventeenth century it could mean to keep hurling missiles at a target. By the nineteenth century it could mean to move rapidly without a pause, as if the feet were beating the ground. Rain and hail took the same image. A downpour pelts because it strikes in a stream of blows. British English still keeps full pelt for an all-out run.
The deeper source of this verb is unsettled, and the standard references disagree in tone. One line takes Middle English pilten back to an unrecorded Old English form, from a medieval Latin verb of beating, and from classical Latin pultare, to beat or knock, a frequentative beside pellere, to push, drive, or strike. That Latin verb is assigned to another Proto-Indo-European root meaning to thrust or drive, not to cover with a hide. The two reconstructed roots happen to look similar in handbooks. They are not the same story.
The Oxford English Dictionary has long been skeptical of that Latin route. Another suggestion starts instead from Old French peloter, to strike with a ball, from pelote, a ball, the source of English pellet. If that is right, the verb pelt is a cousin of pellet, not of pellis. The evidence is not strong enough to close the case. What can be said with confidence is negative and useful: the verb that pelts a window with gravel is not a figurative use of the furrier's noun. Stories that join the two through some image of beating a hide are later inventions.
Keep the two apart
English often lets unrelated words collapse into one spelling once endings wear down. Pelt is a compact example. The hide belongs with Latin pellis, French pel, and the fur-trade vocabulary of medieval England. The barrage belongs with late Middle English striking verbs, and perhaps with Latin beating-words or with French balls, depending on which etymologist you trust. Keep the two apart and the history stays honest. Mix them, and a tidy story appears that the records do not support.
A practical test still works in the living language. If you can substitute hide or skin, you are in the Romance family that gave English the furrier's noun. If you can substitute bombard, beat down, or tear along, you are in the other. The phrase at full pelt is the striking verb wearing a noun's clothes, a speed metaphor dated to the nineteenth century, not a picture of an animal's coat.