1. Made weak or weaker
   "The weakened immune system was more susceptible to infections"
    
2. Reduced in strength
   "the weakened tones of an old recording";
   - attenuate, attenuated, faded
    
3. Damaged; used of inanimate objects or their value
   "The weakened infrastructure needed immediate attention";
   - hurt
    
4. Impaired by diminution
   "Her weakened immune system made her susceptible to infections";
   - diminished, lessened, vitiated

1. Lessen the strength of
   "The fever weakened his body"
    
2. Become weaker
   "The prisoner's resistance weakened after seven days"
    
3. Lessen in force or effect
   "weaken a shock";
   - dampen, damp, soften, break
    
4. Act to reduce, damage or destroy the effectiveness, power or stability of something
   "The Resistance weakened railway operations during the war";
   - sabotage, undermine, countermine, counteract, subvert

See also: damaged, decreased, impaired, reduced, weak

Type of: alter, blunt, change, come down, deaden, decrease, dent, diminish, disobey, fall, go down, lessen, modify, sink

Antonym: fortify, strengthen