What is the meaning of counteract?

verb

• Act in opposition to.
  • synonyms: antagonize, antagonise
• Oppose or check by a counteraction.
  • synonyms: countercheck
• Oppose and mitigate the effects of by contrary actions.
  • usage: "This will counteract the foolish actions of my colleagues"
  • synonyms: countervail, neutralize, counterbalance
• Destroy property or hinder normal operations.
  • usage: "The Resistance sabotaged railroad operations during the war"
  • synonyms: sabotage, undermine, countermine, subvert, weaken