Cap

• environment

1. A layer of clay, or other impermeable material installed over the top of a closed landfill to prevent entry of rainwater and minimize leachate.
   Source: Terms of the Environment

• geology

1. A detonator or blasting cap. Nelson
2. To seal, plug, or cover a borehole. Long
3. The roof or top piece in a three-piece timber set used for tunnel support. Nichols, 1
4. A piece of plank or timber placed on top of a prop, stull, or post. Long
5. The horizontal member of a set of timber used as a roadway support. Nelson
6. Another name for crown. ASTM
7. Barren rock and/or soil covering an ore deposit. See also: cap rock Long
8. Overburden consisting of unconsolidated material overlying or covering bedrock. Also called cover; mantle. Syn: top
9. See: blue cap
   Source: Dictionary of Mining, Mineral, and Related Terms