the world > space > relative position > low position > [noun] > condition of being placed under > that which lies under > underlying layer (7)
The substratum or substrate of something.
An underlying layer or substance; a layer of something below another.
concrete. A foundation, an underlayer.
Materials Science. Any bulk phase or material to which a film, coating, etc., is applied.
Carpet underlay; material laid beneath roofing tiles, etc.