from The American Heritage® Dictionary of the English Language, 5th Edition.

  • transitive verb To weaken by wearing away a base or foundation.
  • transitive verb To weaken, injure, or impair, often by degrees or imperceptibly; sap.
  • transitive verb To dig a mine or tunnel beneath.

from The Century Dictionary.

  • To form a mine under; sap; render unstable by digging or wearing away the foundation of; make an excavation beneath, especially for the purpose of causing to fall, or of blowing up: as, to undermine a wall; a river undermines its banks.
  • Figuratively, to subvert by removing clandestinely the foundation of; injure by invisible, secret, or dishonorable means.
  • To injure, weaken, or destroy insidiously or indirectly; wear away; wear out; sap.
  • noun Same as mine, 2 .
  • noun A cave.

from the GNU version of the Collaborative International Dictionary of English.

  • transitive verb 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.
  • transitive verb Fig.: To remove the foundation or support of by clandestine means; to ruin in an underhand way.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • verb destroy property or hinder normal operations
  • verb hollow out as if making a cave or opening


from Wiktionary, Creative Commons Attribution/Share-Alike License

From under- +‎ mine.


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  • to weaken (usually paired with an abstract term)

    The student undermined the teacher’s authority by questioning the teacher’s judgment on numerous occasions.

    October 11, 2016