The Collaborative International Dictionary of English v.0.48:

Countermine \Coun"ter*mine`\ (koun"t[~e]r*m[imac]n`), n.
   [Counter- + mine underground gallery: cf. F. contermine.]
   1. (Mil.) An underground gallery excavated to intercept and
      destroy the mining of an enemy.
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   2. A stratagem or plot by which another sratagem or project
      is defeated.
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            Thinking himself contemned, knowing no countermine
            against contempt but terror.          --Sir P.
                                                  Sidney.
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The Collaborative International Dictionary of English v.0.48:

Countermine \Coun`ter*mine"\ (koun`t[~e]r*m[imac]n"), v. t. [Cf.
   F. contreminer.] [imp. & p. p. Countermined; p. pr. & vb.
   n. Countermining.]
   1. (Mil.) To oppose by means of a countermine; to intercept
      with a countermine.
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   2. To frustrate or counteract by secret measures.
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The Collaborative International Dictionary of English v.0.48:

Countermine \Coun`ter*mine"\, v. i.
   To make a countermine or counterplot; to plot secretly.
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         'Tis hard for man to countermine with God. --Chapman.
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WordNet (r) 3.0 (2006):

countermine
    n 1: (military) a tunnel dug to defeat similar activities by the
         enemy
    v 1: destroy property or hinder normal operations; "The
         Resistance sabotaged railroad operations during the war"
         [syn: sabotage, undermine, countermine, counteract,
         subvert, weaken]
    2: destroy enemy mines with one's own mines; "We countermined
       the banks of the river"