tree hugger vs treehugger

tree hugger

noun
  • A hippie. 

  • An environmental campaigner, especially one who aims to restrict logging. 

treehugger

noun
  • A species of libellulid dragonfly, Tyriobapta torrida, of Southeast Asia. 

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