underlay

A layer (of earth, etc.) that lies under another; substratum.

A soft floor covering that lies under a carpet.

Anything that is underlaid.

(historical) A piece of paper pasted under woodcuts, stereotype plates, etc. in a form, to bring them up to the necessary level for printing.

Lyrics; or more specifically, the way in which lyrics are assigned to musical notes.

To lay (something) underneath something else; to put under.

To provide a support for something; to raise or support by something laid under.

To put a tap on (a shoe).

To incline from the vertical.