collision vs pile-up

collision

noun
  • An instance of colliding. 

  • Any event in which two or more bodies exert forces on each other in a relatively short time. In a collision, physical contact of two bodies is not necessary. 

pile-up

noun
  • An accumulation that occurs over time, especially one which is not welcome. 

  • A pile of tackling players. 

  • A pile of crashed vehicles due to a traffic accident. 

How often have the words collision and pile-up occurred in a corpus of books? (source: Google Ngram Viewer )