aptness vs lack

aptness

noun
  • disposition of the mind; propensity 

  • suitability; the quality of being apt or suitable 

  • speed or readiness in learning; docility 

  • proneness; tendency 

lack

noun
  • A deficiency or need (of something desirable or necessary); an absence, want. 

verb
  • To be short (of or for something). 

  • To be without, not to have, to need, to require. 

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