weaken in WordNet English dictionary

1. lessen in force or effect
   "soften a shock"; "break a fall"
   dampen  damp  soften  weaken  break 
   
2. destroy property or hinder normal operations
   "The Resistance sabotaged railroad operations during the war"
   sabotage  undermine  countermine  counteract  subvert  weaken 
   
3. reduce the level or intensity or size or scope of
   "de-escalate a crisis"
   de-escalate  weaken  step down 
   
4. become weaker
   "The prisoner's resistance weakened after seven days"
   weaken 
   
5. lessen the strength of
   "The fever weakened his body"
   weaken