drilling rig vs semi

drilling rig

noun
  • An oil rig. 

  • Used other than figuratively or idiomatically: see drilling, rig. 

semi

noun
  • A semi-trailer; a tractor-trailer; an eighteen-wheeler; an artic. 

  • A semifinal. 

  • A semi-detached house. 

  • A partial erection of the penis. 

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