schoolwork vs substructure

schoolwork

noun
  • Work done for school, including both in class and homework. 

substructure

noun
  • The earth or gravel that the railway tracks are embedded in. 

  • Synonym of base (“the forces and relations of production that produce the necessities and amenities of life”) 

  • The supporting part of a structure (either physical or organizational; the foundation). 

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