aetiology vs explanation

aetiology

noun
  • The establishment of a cause, origin, or reason for something. 

  • A cause of disease or of any particular case of a disease (but see pathology § Usage notes). 

  • The study or investigation of the causes of disease; a scientific explanation for the origin of a disease. 

  • The study of causes or causation. 

explanation

noun
  • The act or process of explaining. 

  • Something that explains, makes understandable. 

  • A resolution of disputed points pursuant to discussion; a mutual clarification of disputed points; reconciliation. 

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