harass vs pester

harass

verb
  • To annoy (someone) frequently or systematically; to pester. 

  • To persistently bother (someone, or a group of people) physically or psychologically when such behaviour is illegal and/or unwanted, especially over an extended period. 

  • To trouble (someone, or a group of people) through repeated military-style attacks. 

  • To put excessive burdens upon (someone); to subject (someone) to anxieties. 

pester

verb
  • To bother, harass, or annoy persistently. 

noun
  • A bother or nuisance. 

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