kelp vs kombu

kelp

noun
  • Any of several large brown algae seaweeds (order Laminariales). 

  • The calcined ashes of seaweed, formerly used in glass and iodine manufacture. 

verb
  • To gather kelp. 

kombu

noun
  • Edible kelp (“a type of brown seaweed”) (from the class Phaeophyceae) used in East Asian cuisine. 

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