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1. Impaired by diminution
   - diminished, vitiated, weakened
    
2. Decreased in severity; made less harsh

1. Become smaller or less in size, extent, or range
   "The amount of homework lessened towards the end of the semester";
   - decrease, diminish, fall
    
2. Make become smaller
   "He lessened his staff";
   - decrease, minify
    
3. Wear off or die down
   "The pain lessened";
   - subside

See also: impaired, mitigated

Type of: alter, change, change magnitude, modify, weaken

Encyclopedia: Lessen