preen vs smoothen

preen

verb
  • To flatter. 

  • To spend time making oneself attractive and admiring one's appearance, e.g. in front of a mirror. 

  • To trim up, as trees. 

  • To improve the appearance of; groom; prettify. 

  • To comb; to make orderly. 

  • To groom; to trim or dress with the beak, as the feathers. 

  • To show off, posture, or smarm. 

  • To pin; fasten. 

noun
  • bodkin; brooch 

  • A forked tool used by clothiers for dressing cloth. 

  • pin 

smoothen

verb
  • To make smooth. 

  • To become smooth. 

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