purchase order vs subsection

purchase order

noun
  • A commercial document issued by a buyer to a seller, indicating the type, quantities and agreed prices for products or services the seller will provide to the buyer. 

subsection

noun
  • A subpart of a legal document such as law. 

  • A defined part of a section. 

  • An informal taxonomic category below section and above family. 

  • A taxonomic rank below the section, but above the species. 

verb
  • To insert subsections (into some text, etc.). 

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