Underlay (verb)

To place or position (something) below or beneath something else.

Origin:

From under- (below) + lay (to place or position).

Examples:

1. He underlaid the carpet with a layer of padding.
2. We underlay the tile with a waterproof membrane.
3. She underlaid the wooden floor with insulation.
4. The new road underlay the old one.
5. I underlay the fabric with a stiffener to give it more body.