equalize vs smoothen

equalize

verb
  • To make the scoreline equal by scoring points. 

  • To clear the ears to balance the pressure in the middle ear with the outside pressure by letting air enter along the Eustachian tubes. 

  • To adjust the balance between frequency components within an electronic signal. 

  • To make equal; to cause to correspond in amount or degree. 

  • Said of a morphism: to pre-compose with each of a parallel pair of morphisms so as to yield the same composite morphism. 

smoothen

verb
  • To make smooth. 

  • To become smooth. 

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