biennial vs seedling

biennial

noun
  • A plant that requires two years to complete its life-cycle, germinating and growing in its first year, then producing its flowers and fruit in its second year, after which it usually dies. 

  • An event that happens every two years. 

adj
  • Lasting for two years. 

  • Happening every two years. 

seedling

noun
  • A young plant grown from seed. 

  • a tree smaller than a sapling. 

  • one grown in a nursery for transplanting. 

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