sapping

1. To drain, suck or absorb from (tree, etc.).
2. To exhaust the vitality of.

verb

To strike with a sap (with a blackjack).

1. To subvert by digging or wearing away; to mine; to undermine; to destroy the foundation of.
2. To pierce with saps.
3. To make unstable or infirm; to unsettle; to weaken.
4. To gradually weaken.

   he saps my energy

5. To proceed by mining, or by secretly undermining; to execute saps.

1. The act by which something is sapped or depleted.
2. The act of excavating trenches.