apropos vs thematic

apropos

adj
  • Of an appropriate or pertinent nature. 

  • by the way, incidental 

prep
  • Regarding or concerning. 

adv
  • To the purpose; appropriately. 

  • By the way. 

  • Timely; at a good time. 

thematic

adj
  • Relating to, or having a theme (“subject”) or a topic. 

  • Relating to a melodic subject. 

  • Of or relating to a theme (“subdivision of the Byzantine empire”). 

  • Of a word stem, ending in a vowel that appears in or otherwise influences the noun or verb's inflection. 

noun
  • A postage stamp that is part of a thematic collection. 

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