apt vs pertaining to

apt

adj
  • Ready; especially fitted or qualified (to do something); quick to learn. 

  • Suitable; appropriate; fit or fitted; suited. 

  • Having a habitual tendency; habitually liable or likely; disposed towards. 

noun
  • An apartment; a flat. 

pertaining to

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