grey matter vs skull

grey matter

noun
  • Brains; a person's ability to think. 

  • A collection of cell bodies and (usually) dendritic connections, in contrast to white matter. 

  • Literal brains as a general substance. 

skull

noun
  • The mind or brain. 

  • A crust formed on the ladle, etc. by the partial cooling of molten metal. 

  • The crown of the headpiece in armour. 

  • A shallow bow-handled basket. 

  • The main bones of the head considered as a unit; including the cranium, facial bones, and mandible. 

  • These bones as a symbol for death; death's-head. 

verb
  • To strike the top of (the ball). 

  • To hit in the head with a fist, a weapon, or a thrown object. 

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