verb (v)

• lessen the strength of(verb.change)

  Example:
  The fever weakened his body.
  

  Antonym:
  beef up, fortify, strengthen
  

  source: wordnet30
• become weaker(verb.change)

  Example:
  The prisoner's resistance weakened after seven days.
  

  Synonym:
  dissolve, fade away, fade out
  Antonym:
  strengthen
  

  source: wordnet30
• destroy property or hinder normal operations(verb.social)

  Synonym:
  counteract, countermine, sabotage, subvert, undermine
  

  source: wordnet30
• reduce the level or intensity or size or scope of(verb.change)

  Synonym:
  de-escalate, step down
  Antonym:
  escalate, intensify, step up
  

  source: wordnet30
• lessen in force or effect(verb.change)

  Synonym:
  break, damp, dampen, soften
  

  source: wordnet30
• To make weak; to lessen the strength of; to deprive of strength; to debilitate; to enfeeble; to enervate; as, to weaken the body or the mind; to weaken the hands of a magistrate; to weaken the force of an objection or an argument.(verb)

  source: webster1913
• To become weak or weaker; to lose strength, spirit, or determination; to become less positive or resolute; as, the patient weakened; the witness weakened on cross-examination.(verb)

  source: webster1913