inaptness vs lack

inaptness

noun
  • Quality of being inapt. 

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 inaptness and lack occurred in a corpus of books? (source: Google Ngram Viewer )