Slight beauty, and a hedge
In present-day English, pretty most often names a modest kind of attractiveness: a face, a room, a stretch of countryside that pleases without claiming grandeur. Speakers frequently rank it below beautiful, and the adjective can tip into faint praise or into sarcasm. Used as an adverb, it means something close to fairly or rather, a degree short of very: pretty good, pretty sure, pretty much. Those two lives of the word, the compliment and the hedge, come from one native adjective.
The origin of the word pretty is inheritance inside English, not a later loan from French or Latin.
A noun for a trick
The adjective is built on English soil. Old English had a noun prætt, sometimes written with a single t, meaning a trick, a wile, or a bit of craft. From that noun speakers formed an adjective: West Saxon prættig, Kentish pretti, and a Mercian form of the same shape. In late Old English the sense was not visual. Glossators render it as cunning, crafty, wily, skillful, astute. It could describe a sly person or a clever animal. The snake in one hymn is pætig in that older way: not lovely, but crafty.
The formation is ordinary. The noun plus the adjective suffix -y is the same pattern that later gives tricky. Middle English spellings include prety, preti, praty, and prati. The surname Pratt is widely taken as a nickname from the noun. English still has a historical noun prat for a trick; the later slang prat for the buttocks, from thieves’ cant, is treated as a separate word.
A Germanic root that stops short
Wiktionary and related reconstructions place the adjective on Proto-West Germanic *prattug and Proto-Germanic *prattugaz, with a cluster of senses around sly, slick, boastful, and deceitful. Behind that sits a Germanic stem *pratt- whose further history is unknown. Germanic words that begin with p- and are not obvious loans are often left without a Proto-Indo-European etymon. Some accounts park them in a pre-Indo-European substrate, which is a polite way of saying the trail ends.
Celtic look-alikes have been offered. Older notes point to Cornish prat for an act or a cunning trick. Later discussion treats Welsh and Cornish forms of that shape as probably taken from Latin, and the jump from deed to trick as too thin to rest a derivation on. A Russian word for delirium that happens to look similar is almost certainly chance resemblance. Nothing solid is gained by forcing a deeper story.
Relatives that kept the old flavor
English did not borrow pretty from its neighbors, but the family is easy to see. Old Norse prettr is a trick; prettugr is tricky. Icelandic prettugur still means deceitful or tricky. Dutch pret is a trick or a joke, and Dutch prettig now means pleasant or nice, with an older sense of sportive or funny. Low German prettig is funny. Frisian pret and Flemish pertig, brisk or clever, belong with them. Swedish spratt, a trick, is sometimes linked through a movable initial s, a pattern known across Indo-European; that link is plausible, not proven. Together the cognates show a North Sea and Scandinavian cluster around trick, sport, and slyness, which English later left behind in everyday use.
A documentary gap
After Old English the adjective thins out. Except in surnames, the thirteenth and fourteenth centuries leave almost no record. The Oxford English Dictionary has long noted several points of obscurity in joining the Old English form to the Middle English one, while still treating them as the same word. When the adjective becomes frequent again in the fifteenth century, it arrives all at once in several senses. None of those senses is identical with the Old English glosses, yet all can be derived from skill and cunning.
That gap matters. It is why a tidy classroom story, Old English pretty already meaning beautiful, is false. The visual sense is a late arrival.
How praise drifted downward
By about 1400 the range includes manly or gallant, ingeniously or cleverly made, and then fine, pleasing to the eye. Around the middle of the fifteenth century it settles on beautiful in a slight, delicate way. The path is a familiar English softening, the same kind of drift seen in nice, silly, canny, cute, and fine: a word for skill or cunning becomes a word for something well made, then for something agreeable, then for something merely attractive. Bees were already pretty around 1400, which shows the adjective leaving people and attaching to small living things.
A late-fifteenth-century sense, now dated, is considerable or moderately large: a pretty while, a pretty sum. From that quantitative use the adverb of degree is a short step. From the 1560s the adverb means to a considerable extent, less than very. Pretty much is in place by the 1660s. A pretty penny for a large amount of money appears in the early eighteenth century.
Irony is early as well. From the 1530s a pretty mess or a pretty pass can mean the opposite of pleasing, the same sarcastic turn that fine can take. The verb to pretty, usually pretty up, is modern, from the early twentieth century. The noun for a pretty person or thing is eighteenth-century.
What later style manuals insisted on, that pretty names a small or undignified beauty and is awkward or contemptuous of men, is a social overlay on that slight-beauty sense, not the medieval starting point.
A cognate that still tells the truth
Dutch speakers still use prettig for pleasant, and Icelandic still uses prettugur for tricky. English kept both ends of that old range, but stacked them in time: first the trick, then the skill, then the small beauty, and at last the hedge in pretty good. The everyday compliment did not need a foreign loan. It needed several centuries of praise sliding from cunning toward charm.