central vs substratal

central

adj
  • Having or containing the centre of something. 

  • Being in the centre. 

  • Exerting its action towards the peripheral organs. 

  • Being very important, or key to something. 

noun
  • centre 

substratal

adj
  • Of or pertaining to a substratum. 

  • Specifically, pertaining to a substrate language. 

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