Meaning

noun single thickness of usually some homogeneous substance

noun a relatively thin sheetlike expanse or region lying over or under another

noun an abstract place usually conceived as having depth

originAppears 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 etymology 2 below. For the pronunciation compare prayer. However, this word layer (referring to a thickness of a material covering a surface) has also been argued to be from a respelling of an obsolete sense of the word lair that was once…

Etymology from Wiktionary, CC BY-SA 3.0