megrim vs sail-fluke

megrim

noun
  • A type of flatfish of the genus Lepidorhombus native to the northeastern Atlantic Ocean; specifically, the Cornish sole, sail-fluke, or whiff (Lepidorhombus whiffiagonis). 

  • See megrims (“depression; any of various diseases of animals”). 

sail-fluke

noun
  • Synonym of megrim (“the Cornish sole or whiff (Lepidorhombus whiffiagonis”) 

How often have the words megrim and sail-fluke occurred in a corpus of books? (source: Google Ngram Viewer )