apprehension vs soul-searching

apprehension

noun
  • Perception; the act of understanding using one's intellect without affirming, denying, or passing any judgment 

  • Opinion; conception; sentiment; idea. 

  • Anticipation, especially of unfavorable things such as dread or fear or the prospect of something unpleasant in the future. 

  • The faculty by which ideas are conceived or by which perceptions are grasped; understanding. 

  • The physical act of seizing or taking hold of (something); seizing. 

  • The act of seizing or taking by legal process; arrest. 

soul-searching

noun
  • Probing introspection; a critical consideration of one's conscience; also, an instance of such consideration. 

adj
  • Involving probing introspection, or a critical consideration of one's conscience, especially motives and values. 

How often have the words apprehension and soul-searching occurred in a corpus of books? (source: Google Ngram Viewer )