let vs permit

let

verb
  • To allow to be or do without interference; to not disturb or meddle with; to leave (someone or something) alone. 

  • To give, grant, or assign, as a work, privilege, or contract; often with out. 

  • Used to introduce a first or third person imperative verb construction. 

  • To cause (+ bare infinitive). 

  • To allow the release of (a fluid). 

  • To allow possession of (a property etc.) in exchange for rent. 

  • To allow to, not to prevent (+ infinitive, but usually without to). 

noun
  • The hindrance caused by the net during serve, only if the ball falls legally. 

  • An obstacle or hindrance. 

  • The allowing of possession of a property etc. in exchange for rent. 

permit

verb
  • To allow (someone) to do something; to give permission to. 

  • To allow (something) to happen, to give permission for. 

  • To allow for, to make something possible. 

  • To allow, to admit (of). 

  • To grant formal authorization for (something). 

  • To attempt to obtain or succeed in obtaining formal authorization for (something). 

noun
  • A pompano of the species Trachinotus falcatus. 

  • An artifact or document rendering something allowed or legal. 

  • A learner's permit. 

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