clustering vs narrowing

clustering

noun
  • The undesirable contiguous grouping of elements in a hash table. 

  • A grouping of a number of similar things. 

  • A prewriting technique consisting of writing ideas down on a sheet of paper around a central idea within a circle, with the related ideas radially joined to the circle using rays. 

  • The grouping of a population based on ethnicity, economics or religion. 

adj
  • Forming a cluster. 

narrowing

noun
  • The part of a stocking that is narrowed. 

  • The process of becoming narrow. 

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