Where does “pestereth” come from?

pestereth (English) comes from English pester, from Old French empestrer — encumber.

pestereth (English): third-person singular simple present indicative...

Definitions

  1. third-person singular simple present indicative...

Ancestry of “pestereth”, step by step

pestereth traces back through two separate lines of ancestry.

via English pester

StepLanguageWordMeaning
1EnglishpesterTo bother, harass, or annoy persistently; To...
2Old Frenchempestrerencumber

via English eth

StepLanguageWordMeaning
1EnglishethA letter introduced into Old English to...
Every word from Old French empestrerEvery word from English pester