bottleneck vs retarder

bottleneck

noun
  • The part of a process that is too slow or cumbersome. 

  • In traffic, any narrowing of the road, especially resulting in a delay. 

  • The narrow portion that forms the pouring spout of a bottle; the neck of a bottle. 

verb
  • To slow by causing a bottleneck. 

  • To form a bottleneck. 

retarder

noun
  • Something which retards or slows. 

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

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

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