v.tr. 1 injure (a person, reputation, influence, etc.) by secret or insidious means. 2 weaken, injure, or wear out (health etc.) imperceptibly or insidiously. 3 wear away the base or foundation of (rivers undermine their banks). 4 make a mine or excavation under. underminer n. underminingly adv.
[ ME f. UNDER- + MINE(2) ]