semi vs trucking rig

semi

noun

  • A semifinal. 

  • A semi-detached house. 

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

  • A partial erection of the penis. 

trucking rig

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