ABCs vs substratum

ABCs

noun
  • The alphabet, especially the English alphabet. 

  • The alphabet. 

  • Letters; writing; the skill of literacy. 

substratum

noun
  • A substrate. 

  • The underlying cause or basis of something. 

  • A layer that lies underneath another. 

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