1. a layer of material placed under something else for support, protection, or cushioning

1. to place something under another thing as support or foundation
2. to form the basis or foundation for something

Examples

• The carpet installer placed a thick underlay beneath the new flooring.
• We need to underlay the weak floorboards with additional support beams.
• The foam underlay provides extra comfort and insulation.
• Strong moral principles underlay all of her decisions.
• The contractor will underlay the foundation with gravel for better drainage.
• A rubber underlay prevents the rug from slipping on the hardwood floor.
• Economic concerns underlay the government’s new policy changes.