sap

1 :  to drain or deprive of sap

2 :  to knock out with a sap

:  to proceed by digging a sap

1 :  to subvert by digging or eroding the substratum or foundation :  undermine

2a :  to gradually diminish the supply or intensity of sapped her strengthb :  to weaken or exhaust the energy or vitality of the illness sapped him of his stamina

3 :  to operate against or pierce by a sap

:  the extension of a trench to a point beneath an enemy's fortifications

:  a watery juice that circulates through a plant and carries food and nutrients

:  to weaken or use up little by little … the heavy load they dragged sapped their strength severely. — Jack London, The Call of the Wild

—see cell sap, nuclear sap