pixie vs water nymph

pixie

noun
  • A playful sprite or elflike or fairy-like creature. 

  • A butterfly of the genus Melanis. 

  • A cute, petite woman with short hair. 

  • An upper-atmospheric optical phenomenon associated with thunderstorms, a short-lasting pinpoint of light on the surface of convective domes that produces a gnome. 

water nymph

noun
  • A female spirit presiding over fountains, wells, streams, etc. 

  • Any of various aquatic plants of the genus Najas. 

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