apprehend vs understand

apprehend

verb
  • To take hold of (something) with understanding; to conceive (something) in the mind; to become cognizant of; to understand. 

  • To be or become aware of (something); to perceive. 

  • To have a conception of (something); to consider, to regard. 

  • To seize or take (something); to take hold of. 

  • To understand. 

  • To be of opinion, believe, or think; to suppose. 

  • To seize or take (a person) by legal process; to arrest. 

  • To be apprehensive; to fear. 

  • To anticipate (something, usually unpleasant); especially, to anticipate (something) with anxiety, dread, or fear; to dread, to fear. 

  • To acknowledge the existence of (something); to recognize. 

understand

verb
  • To grasp a concept fully in one's mind, especially (of words, statements, art, etc.) to be aware of the meaning of and (of people) to be aware of the intent of. 

  • To believe, to think one grasps sufficiently despite potentially incomplete knowledge. 

  • To stand underneath, to support. 

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