featherweight vs unheavy

featherweight

noun
  • A sportsman who fights in this division. 

  • A weight class in many combat sports; e.g. in professional boxing of a maximum of 126 pounds or 57.2 kilograms. 

  • The lightest weight that may be carried by a racehorse. 

unheavy

adj
  • Not heavy. 

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