helper vs railway carriage

helper

noun
  • A locomotive that assists a train, usually on steep gradients. 

  • That which helps; anything serving to assist. 

  • One who helps; an aide; assistant; auxiliary. 

  • A person who does cleaning and cooking in a family home, or in a market; domestic employee. 

railway carriage

noun
  • A railroad car (for passengers) 

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