A catch-all that used to be more specific
In present-day English, stuff is the everyday name for things you do not bother to name. It covers belongings, materials, odds and ends, and, more loosely, affairs in general: do some stuff, the right stuff, kitchen stuff. The verb is just as ordinary. To stuff a bag, a turkey, or a ballot box is to pack something full, sometimes to excess.
That vagueness is late. For a long stretch of its English life the word pointed at particular kinds of material and supply, not at everything on a desk.
A French loan in Middle English
Stuff is not an inherited Old English word. It arrived as a borrowing in the Middle English period, taken from Old French estoffe (modern French étoffe) and from the related verb estoffer or estofer. Anglo-French forms such as estuffe sat beside Latinized stuffa in administrative writing, which helps explain why English settled on a short form without the opening vowel of the French noun.
The Oxford English Dictionary places the noun in Middle English and cites evidence from around 1330 in the work of Robert Mannyng. Other dictionaries group the first English uses in the first half of the fourteenth century. The verb follows in the same century: Middle English stuffen meant to furnish a place with goods or provisions, and to reinforce a stronghold with men. Anglo-Norman records of estuffer already show that military sense of stocking a town or castle, as well as packing a ship with food.
French still keeps the older, narrower picture more clearly than English does. Étoffe is first of all fabric. The verb étoffer still means to furnish or to give body to something. English kept those senses for a time, then let the noun drift toward a general heap of things.
Quilt, stores, and cloth
The earliest English noun was not a synonym for belongings. Around the early fourteenth century, stuffe could mean the quilted fabric worn under chain mail: padding that filled out armor rather than a pile of objects. From there the word spread into the language of work. By about 1400 it named material a craftsman worked with. Early in the next century it covered military stores: arms, rations, gear. By the middle of the fifteenth century it could mean movable property, household goods, farm stock, cargo, and foodstuffs.
Cloth remained a durable strand. For centuries a stuff was a woven textile, especially a woollen cloth used for ordinary clothing. Building boards, parchment, and other raw materials also sat under the same heading. In that older usage, stuff is closer to French étoffe than to the modern shrug of whatever is lying around.
The verb tracked the same physical idea. Late in the fourteenth century it already meant to pad a mattress or to fill pastry and a fowl. Around 1400 it broadened to cramming any loose filling into a space, including filling the belly. Clogging the sinuses appears in the fifteenth century. Taxidermy, filling a prepared skin, is recorded in the sixteenth. American English later applied the same image to stuffing a ballot box.
What the word is made of
English did not build stuff from a native prefix and root. It took a ready-made French pair, noun and verb, and the two kept feeding each other. Dictionaries disagree on which came first on the Continent. The noun may be a derivative of the verb, or the verb may rest on the noun. Italian stoffo and Portuguese estofo, used of quilted material, look like verbal nouns, which is one reason some accounts treat the verb as the older member of the pair.
The step behind French is the real argument. Many French and English handbooks derive estoffer from a Germanic verb: Old High German stopfon, to plug or cram, or a related Frankish form reconstructed as stopfōn or stoppōn. That family is the same one that yields German stopfen and, on the usual view, English stop. Wiktionary traces the chain further to Proto-West Germanic stoppōn, to block or fill.
The Oxford English Dictionary has long called that Germanic source open to strong objections. A specifically High German etymon is an awkward donor for a word shared across Romance. The oldest Romance meaning also looks like furnishing or stocking, not plugging a hole with oakum. A rival explanation links the Germanic plug-verbs themselves to Vulgar Latin stuppare, from Latin stuppa, coarse flax or tow, because tow was used as a stopper. Phonetics can be made to fit; the meanings do not line up as neatly, and some scholars would rather treat the Germanic stop-group as native. The honest position is that English borrowed a French word whose earlier history is still unsettled.
Cognates on the Romance and later Germanic side are clearer. Italian stoffa, Spanish and Portuguese estofa, Dutch stof, German Stoff, Swedish stoff, and Danish stof all sit in the same cluster. German Stoff still means both fabric and matter, a split that English once shared and then partly abandoned in ordinary speech.
From padding to character
Once stuff could mean any working material, it was a short step to unnamed substance. By the mid-fifteenth century the noun already named matter of an unspecified kind, physical or abstract. In the later sixteenth century it could mean the substance a thing consists of, and, figuratively, what a person is made of. That is the line behind sterner stuff and the right stuff: character spoken of as if it were cloth or timber.
The same widening produced a dismissive sense. From the 1570s the word could mean empty talk; stuff and nonsense is eighteenth-century English for the same shrug. In the twentieth century, to know one’s stuff meant to have a real command of a subject, turning the old idea of working material into professional competence.
The modern informal noun is the end of that widening, not a separate coinage. When English speakers call a room full of objects stuff, they are using a fourteenth-century loan that first named quilted lining, then stores and cloth, then matter in general. The verb never quite forgot the older job of packing a space until it would hold no more.
French étoffe stayed close to fabric. English let the same loan become the default word for whatever is on hand. That gap is the most useful fact about the history: a word that now means almost anything entered the language as a name for material you could cut, store, or sew under armor.