Deadhead vs mourning

Deadhead

noun
  • A fan of the rock band The Grateful Dead. 

mourning

noun
  • Feeling or expressing sorrow over someone's death. 

  • The traditional clothes worn by those who mourn (in Western societies, typically coloured black). 

  • The act of expressing or feeling sorrow or regret; lamentation. 

  • Drapes or coverings associated with mourning. 

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