drill into vs entrench

drill into

entrench

verb
  • To surround or provide with a trench, especially for defense; to dig in. 

  • To establish a substantial position in business, politics, etc. 

  • To dig or excavate a trench; to trench. 

  • To invade; to encroach; to infringe or trespass; to enter on, and take possession of, that which belongs to another; usually followed by on or upon. 

  • To cut in; to furrow; to make trenches in or upon. 

  • To become completely absorbed in and fully accept one's beliefs, even in the face of evidence against it and refusing to be reasoned with. 

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