lemongrass vs lemongrass oil

lemongrass

noun
  • Sourgrass, Oxalis pes-caprae. 

  • One of various species of grass of the genus Cymbopogon, especially Cymbopogon citratus, which have a lemon-like taste and aroma, and are used in cooking, for tea, and for fragrance. 

lemongrass oil

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