aptness vs grey matter

aptness

noun
  • disposition of the mind; propensity 

  • suitability; the quality of being apt or suitable 

  • speed or readiness in learning; docility 

  • proneness; tendency 

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. 

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