coequal vs synonymous

coequal

adj
  • Equal to each other in size, rank or position. 

noun
  • An equal person or thing. 

synonymous

adj
  • Having an identical meaning. 

  • Having a similar meaning. 

  • Such that both its forms yield the same sequenced protein. 

  • Of, or being a synonym. 

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