chokepoint vs retarder

chokepoint

noun
  • A point at which traffic or other movement can easily become blocked. 

retarder

noun
  • A device for slowing down large trucks, lorries, buses, shunted railway wagons. 

  • Something which retards or slows. 

  • A refrigerator used to slow down proofing of yeast when making dough. 

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