let out vs unbolt

let out

verb
  • To enlarge by adjusting one or more seams. 

  • Of a school: to finish for the day or term, allowing the pupils to go home. 

  • To disclose. 

  • To rent out. 

  • Of sound, to emit. 

  • To allow to operate at higher speed by adjusting controls. 

  • To release. 

unbolt

verb
  • To unlock by undoing the bolts of. 

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