lessening vs reducer

lessening

noun
  • A growing lesser; reduction or decrease. 

reducer

noun
  • Something that reduces. 

  • A reducing agent. 

  • A liquid used in the process of developing a negative to reduce its darkness. 

  • A function that takes state and action as arguments and returns the next state of the app. 

  • A hydraulic device for reducing pressure and hence increasing movement, used to transmit the load from the hydraulic support of the lower shackle to the lever weighing apparatus in some kinds of heavy testing machine. 

  • A component used to connect two pipes of different bores. 

How often have the words lessening and reducer occurred in a corpus of books? (source: Google Ngram Viewer )