realize vs understand

realize

verb
  • To sense vividly or strongly; to make one's own in thought or experience. 

  • To become aware of (a fact or situation, especially of something that has been true for a long time). 

  • To cause to seem real to other people. 

  • To turn an abstract linguistic object into actual language, especially said of a phoneme's conversion into speech sound. 

  • To make real; to convert from the imaginary or fictitious into reality; to bring into real existence 

  • To acquire as an actual possession; to obtain as the result of plans and efforts; to gain; to get 

  • To convert any kind of property into money, especially property representing investments, such as shares, bonds, etc. 

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 realize and understand occurred in a corpus of books? (source: Google Ngram Viewer )