Law is Norse. Old English had its own words, ae and gesetnes, and law ousted them both — a rare thing, since a language does not usually borrow its word for law unless the borrowing is happening at close quarters. It came from Old Norse, from lag, "layer, measure, something laid down," a collective plural meaning literally "that which is fixed or set."
The metaphor underneath is worth having: a law is something laid down, in the same physical sense as a layer. That makes the modern word a twin of the native lay, from the same Indo-European root meaning "to lie down, to lay." The Danelaw settlement left English an enormous amount of this kind of vocabulary — they, them, take, want, knife, skin, sky — but law is the one that most clearly shows Norse speakers and English speakers running institutions together. The scientific sense, a proposition expressing a regular order of phenomena, is from the 1660s.
law (n.) Middle English laue , from Old English lagu (plural laga , combining form lah- ) "ordinance, rule prescribed by authority, regulation; district governed by the same laws;" also sometimes "right, legal privilege," from Old Norse *lagu "law," collective plural of lag "layer, measure, stroke," literally "something laid down, that which is fixed or set." This is reconstructed to be from Proto-Germanic *lagam "put, lay" (from PIE root *legh- "to lie down, lay"). The modern word is thus a twin of lay (n.2) as "that which is set or established." Rare in Old English, law ousted the more usual ae and also gesetnes , which, with law , also meant etymologically "something placed or set." In physics, from 1660s as "a proposition which expresses the constant or regular order of certain actions or phenomena," often named for the formulator of it ( Bode , Grimm , Murphy , etc.). Law of the land "established law of a country" is attested from c.1300. Law and order have been coupled since c. 1600. To lay down the law (1690s) is pleonastic (the "law" in the figure is biblical law, laid down from the pulpit or by God). Poor laws provided for the support of paupers at public expense; sumptuary laws restrained excesses in apparel, food, or luxuries. It is essential to the idea of a law that it be attended with a sanction; or, in other words, a penalty or punishment for disobedience. [Hamilton, "Federalist," No. 15] [L]earn to obey good laws before you seek to alter bad ones [Ruskin, "Fors Clavigera"] * Indo-European languages commonly use different words for "a specific law" and for "law" in the general sense of "institution or body of laws; principles and regulations of human government in their application to property and conduct," for example Latin lex "a law," but ius "a right," especially "legal right, law." The Indo-European words for "a law" are commonly from verbs for "to put, place, set, lay," such as Greek thesmos (from tithemi "to put, place"), Old English dom (modern doom , from PIE *dhe- "to put, place, set"), Lithuanian įstatymas (from statyti "cause to stand, set up, establish"), Polish ustawa (from stać "stand"). Also compare statute , from Latin statuere , and German Gesetz "a law, statute," from Old High German gisatzida "a fixing, determination, assessment," with sezzen (modern German setzen ) "to make sit, set, put." The formation parallela that of Old English gesetnes (above). The words for "law" in the general sense mostly mean etymologically "what is right" and often are connected with adjectives for "right" (themselves often figurative uses of words for "straight," "upright," "true," "fitting," or "usage, custom"). Such are Greek nomos (as in numismatic ); French droit , Spanish derecho , from Latin directus ; Polish prawo , Russian pravo (from Old Church Slavonic pravŭ "straight," in the daughter languages "right"); also Old Norse rettr , Old English riht , Dutch recht , German Recht (see right (adj.1)). law (v.) 1640s, "to litigate," from law (n.). Old English had lagian "make a law, ordain." Related: Lawed ; lawing . also from 1640s
law came in through Old Norse, and its spelling follows that family's conventions.
What gives it away on the page
| core vocabulary that isn't Old English | Borrowing pronouns is rare and marks deep contact, not fashion.they, them, their, are, take, want, die, knife, window, law |
Placing it without the spelling
| blunt everyday things — and a few words too basic to look borrowed | Old Norsesky, knife, window, law |
Old Norse in the spelling guide · guess another word's family