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, it ousted the more usual ae and also gesetnes, which also were etymologically “something placed or set.” 

In physics, “a proposition which expresses the regular order of things,” from 1660s. Law and orderhave been coupled since 1796. To lay down the law(1752) is pleonastic (the “law” in the figure is biblical law, laid down from the pulpit). Poor laws provided for the support of paupers at public expense; sumptuary laws restrained excesses in apparel, food, or luxuries.

It is more common for Indo-European languages to use different words for “a specific law” and for “law” in the general sense of “institution or body of laws,” for example Latin lex “a law,” ius “a right,” especially “legal right, law.”

Indo-European words for “a law” are most commonly from verbs for “to put, place, set, lay,” such as Greek thesmos (from tithemi “to put, place”), Old English dom (from PIE *dhe- “to put, place, set”), Lithuanian įstatymas (from statyti “cause to stand, set up, establish”), Polish ustawa (from stać “stand”). Also compare Old English gesetnes (above), statute, from Latin statuere; German Gesetz “a law, statute,” from Old High German gisatzida “a fixing, determination, assessment,” with sezzen (modern German setzen) “to make sit, set, put.”

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)).

Source: https://www.etymonline.com/word/law#

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Ecclesiastical

Law.—

I. CONCEPT OF LAW

A. Widest Sense

By law in the widest sense is understood that exact guide, rule, or authoritative standard by which a being is moved to action or held back from it. In this sense we speak of law even in reference to creatures that are incapable of thinking or willing and to inanimate matter. The Book of Proverbs (ch. viii) says of Eternal Wisdom that it was present when God prepared the heavens and when with a certain law and compass He enclosed the depths, when He encompassed the sea with its bounds and set a law to the waters that they should not pass their limits. Job (xxviii, 25 sqq.) lauds the wisdom of God Who made a weight for the winds and weighed the water by measure, Who gave a law for the rain and a way for the sounding storms.

Daily experience teaches that all things are driven by their own nature to assume a determinate, constant attitude. Investigators of the natural sciences hold it to be an established truth that all nature is ruled by universal and constant laws and that the object of the natural sciences is to search out these laws and to make plain their reciprocal relations in all directions.

To read the length of the definition under Catholic encyclopedia see Source: https://www.catholic.com/encyclopedia/law

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