blowoff vs touch hole

blowoff

noun
  • The explosive separation of part of a rocket etc in order to prevent its destruction and allow for retrieval 

  • Something that is blown off. 

  • A fart. 

  • An outburst of temper or excitement. 

  • A blowing off of steam, water, etc. 

touch hole

noun
  • A small hole through which the propellant charge of a cannon or muzzleloading gun is ignited. 

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