v. t. 1. 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. [ 1913 Webster ] A vast rock undermined from one end to the other, and a highway running through it. Addison. [ 1913 Webster ] 2. Fig.: To remove the foundation or support of by clandestine means; to ruin in an underhand way; as, to undermine reputation; to undermine the constitution of the state. [ 1913 Webster ] He should be warned who are like to undermine him. Locke. [ 1913 Webster ] | 