butter bean vs common bean

butter bean

noun
  • Any of several beans, including the lima bean, sieva bean, wax bean, and civet bean. 

common bean

noun
  • An herbaceous annual plant (Phaseolus vulgaris), grown for its edible bean. 

  • A bean of such a plant, varying in size, shape and especially color. 

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