Layer
Middle English (denoting a mason): from lay1 + -er1. The sense ‘stratum of material covering a surface’ (early 17th century) may represent a respelling of an obsolete agricultural use of lair1 denoting quality of soil.
wiktionary
Appears at first glance to be from Middle English leyer, leyare(“a layer of stones or bricks”), equivalent to lay + -er. In which case, ultimately identical to the other word below that is also spelt layer.
However, this word layer (referring to a thickness of a material covering a surface) has long been argued to be from a respelling of an obsolete sense of the word lair that was once used by farmers, which had to do with soil. The connecting sense between the usual meaning of lair and the specialised farming meaning was: an area where cows typically rest, the ground being fertilised by their waste. Related to lie, ledger.
lay + -er
etymonline
layer (n.)
late 14c., "one who or that lays" (especially stones, "a mason"), agent noun from lay (v.). Passive sense of "a thickness of some material laid over a surface" is first recorded 1610s, but because the earliest English use was in cookery this is perhaps from French liue "binding," used of a thickened sauce. Of hens from 1707. Layer cake attested from 1875.
layer (v.)
1832, in gardening, as a method of plant propagation, from layer (n.). Meaning "to form into layers" is from 1852. Related: Layered; layering.
