undermine

v. (-ning) 1 injure (a person, reputation, health, etc.) Secretly or insidiously. 2 wear away the base of (banks were undermined). 3 make an excavation under.

v. t. To excavate the earth beneath, or the part of, especially for the purpose of causing to fall or be overthrown; to form a mine under; to sap; as, to undermine a wall.