irritant vs placation

irritant

adj
  • Causing irritation or inflammation. 

  • Rendering null and void; conditionally invalidating. 

noun
  • Any medication designed to cause irritation 

  • A source of irritation. 

placation

noun
  • A process or act of placating; appeasement or an expression of appeasement. 

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