extensional vs perspicuous

extensional

adj
  • Having great extent. 

  • Of or pertaining to extension. 

perspicuous

adj
  • Clearly expressed, easy to understand; lucid. 

  • (Of a language or notation) the process of inference from premises to conclusion is explicitly laid out. 

  • Transparent; translucent. 

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