pilot whale vs porpoise

pilot whale

noun
  • Either of two species of whale in the genus Globicephala, dark grey in colour. 

porpoise

noun
  • A small cetacean of the family Phocoenidae, related to dolphins and whales. 

  • Any small dolphin. 

verb
  • Said of an air-breathing aquatic animal such as a porpoise or penguin: To repeatedly jump out of the water to take a breath and dive back in a continuous motion. 

  • Said of an aircraft: to make a series of plunges when taking off or landing; or of a watercraft: to successively plunge up and down in the water. 

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