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1. Act in opposition to
   - antagonize, antagonise [Brit]
    
2. Oppose or check by a counteraction
   - countercheck
    
3. Oppose and mitigate the effects of by contrary actions
   "This will counteract the foolish actions of my colleagues";
   - countervail, neutralize, counterbalance, neutralise [Brit]
    
4. Destroy property or hinder normal operations
   "The Resistance counteracted railway operations during the war";
   - sabotage, undermine, countermine, subvert, weaken

Derived forms: counteracts, counteracting, counteracted

Type of: act, cancel, check, contain, control, curb, disobey, hold, hold in, moderate, move, offset, set off