dirk vs pocketknife

dirk

noun
  • A long Scottish dagger with a straight blade. 

verb
  • To stab with a dirk. 

pocketknife

noun
  • A knife with blades or tools that the user can fold or retract into its handle, and of a size small enough for carrying safely and handily in a pocket, especially when suited to heavier duty uses or ad hoc applications outdoors or in workshops. 

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