green bean vs string bean

green bean

noun

  • The immature pods of numerous varieties of the common bean, Phaseolus vulgaris. 

  • The immature pods of any kind of bean plant, eaten as a vegetable. 

string bean

noun

  • A common bean (Phaseolus vulgaris) 

  • A hyacinth bean (Lablab purpureus) 

  • Any long, slender green bean. 

  • A tall and thin person. 

  • An immature runner bean (Phaseolus coccineus) 

  • A yardlong bean (Vigna unguiculata subsp. sesquipedalis) 

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