lessen in WordNet English dictionary

1. decrease in size, extent, or range
   "The amount of homework decreased towards the end of the semester"; "The cabin pressure fell dramatically"; "her weight fell to under a hundred pounds"; "his voice fell to a whisper"
   decrease  diminish  lessen  fall 
   
2. make smaller
   "He decreased his staff"
   decrease  lessen  minify 
   
3. wear off or die down
   "The pain subsided"
   subside  lessen