naiad vs water nymph

naiad

noun
  • Any of various aquatic plants of the genus Najas. 

  • A female deity (nymph) associated with water, especially a spring, stream, or other fresh water. 

  • The aquatic larva (nymph) of a dragonfly or damselfly. 

water nymph

noun
  • Any of various aquatic plants of the genus Najas. 

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

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