let in in WordNet English dictionary

1. allow participation in or the right to be part of; permit to exercise the rights, functions, and responsibilities of
   "admit someone to the profession"; "She was admitted to the New Jersey Bar"
   admit  let in  include 
   
2. allow to enter; grant entry to
   "We cannot admit non-members into our club building"; "This pipe admits air"
   admit  allow in  let in  intromit 
   

let in in English Wiktionary