underlay

Short definition from Wiktionary

Verb

1. 1
   simple past of underlie
2. 2
   To lay (something) underneath something else; to put under.
3. 3
   To provide a support for something; to raise or support by something laid under.
4. 4
   To put a tap on (a shoe).
5. 5
   To incline from the vertical.

Noun

1. 1
   A layer (of earth, etc.) that lies under another; substratum.
2. 2
   A soft floor covering that lies under a carpet.
3. 3
   Anything that is underlaid.
4. 4
   A piece of paper pasted under woodcuts, stereotype plates, etc. in a form, to bring them up to the necessary level for printing.
5. 5
   Lyrics; or more specifically, the way in which lyrics are assigned to musical notes.