lessen vs propagate

lessen

conj
  • unless. 

verb
  • To make less; to diminish; to reduce. 

  • To become less. 

propagate

verb
  • To cause to take effect on all relevant devices in a network. 

  • To spread from person to person; to extend the knowledge of; to originate and spread; to carry from place to place; to disseminate. 

  • To produce young; to be produced or multiplied by generation, or by new shoots or plants. 

  • To cause to spread to extend; to impel or continue forward in space. 

  • To cause to continue or multiply by generation, or successive production. 

  • To generate; to produce. 

  • To take effect on all relevant devices in a network. 

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