abdomen vs below the belt

abdomen

noun
  • The posterior section of the body, behind the thorax, in insects, crustaceans, and other Arthropoda. 

  • The cavity of the belly, which is lined by the peritoneum, and contains the viscera; often restricted in humans to the part between the diaphragm and the commencement of the pelvis, the remainder being called the pelvic cavity. 

  • The belly, or that part of the body between the thorax and the pelvis, not including the back; or in some lower vertebrates, the portion between the cardiac and caudal regions. 

below the belt

prep
  • Of a punch, landing illegally, below the opponent's waist. 

  • Unfair; dirty; not according to the generally accepted rules. 

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