Old English lagu (plural laga, comb. form lah-) "law, ordinance, rule, regulation; district governed by the same laws," from Old Norse *lagu "law," collective plural of lag "layer, measure, stroke," literally "something laid down or fixed," from Proto-Germanic *lagan "put, lay" (see lay (v.)).
Replaced Old English æ and gesetnes, which had the same sense development as law. Cf. also statute, from Latin statuere; German Gesetz "law," from Old High German gisatzida; Lithuanian istatymas, from istatyti "set up, establish." In physics, from 1660s. Law and order have been coupled since 1796.