layer (n.) Look up layer at Dictionary.com
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 1881.
layer (v.) Look up layer at Dictionary.com
1832, in gardening, as a method of plant propagation, from layer (n.). Meaning "to form into layers" is from 1852. Related: Layered; layering.