BTM vs caboose

BTM

noun
  • bottom 

caboose

noun
  • buttocks 

  • The person or team in last place. 

  • A youngest child who is born after a long gap in time. 

  • A small sand-filled container used as an oven on board ship. 

  • The last car on a freight train, having cooking and sleeping facilities for the crew; a guard’s van. 

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