To sap; to excavate the earth beneath, for the purpose of suffering to fall, or of blowing up; as, to undermine a wall.

To excavate the earth beneath. Rapid streams often undermine their banks and the trees growing upon’ them.

To remove the foundation or support of any thing by clandestine means; as, to undermine reputation; to undermine the constitution of the state. He should be warned who are like to undermine him.