prime mover vs road train

prime mover

noun
  • The front part of a semi-trailer type truck, i.e., the tractor to which the trailer part attaches. 

  • A person or thing that is seminal and influential. 

  • A military or heavy construction vehicle. 

  • The initial agent that is the cause of all things. 

  • A machine, such as a water wheel or steam engine, that receives and modifies energy as supplied by some natural source or fuel and transforms it into mechanical work 

road train

noun
  • A transport concept consisting of a conventional prime mover truck pulling two or more trailers. 

How often have the words prime mover and road train occurred in a corpus of books? (source: Google Ngram Viewer )