Underlay v. t. : To lay beneath; to put under.

Underlay v. t. : To raise or support by something laid under; as, to underlay a cut, plate, or the like, for printing. See Underlay, n., 2.

Underlay n. : To put a tap on (a shoe).

Underlay v. i. : To incline from the vertical; to hade; -- said of a vein, fault, or lode.

Underlay n. : The inclination of a vein, fault, or lode from the vertical; a hade; -- called also underlie.

Underlay n. : A thickness of paper, pasteboard, or the like, placed under a cut, or stereotype plate, or under type, in the from, to bring it, or any part of it, to the proper height; also, something placed back of a part of the tympan, so as to secure the right impression.

Example:
How do I clean a woollen Underlay?

Taxonomy
Underlay, thin layer, floor, free encyclopedia, underlayment, level floor, The Oxford English Dictionary, 2nd ed, flooring products, vinyl flooring, search, provide comfort, carpet, insulation, moisture, plywood, uniform, platform.

Defination from the web:
underlay is the thin layer of plywood that is fastened over the structural sub-floor to create a uniform, smooth, ... For laminated wood flooring the underlay provides a "vapor barrier" to prevent moisture from coming through the floor of the home and migrating ...