copilot vs skipper

copilot

verb
  • To serve as relief or assistant pilot. 

noun
  • A backup or assistant pilot of an aircraft. 

skipper

verb
  • To captain a ship or a sports team. 

  • To take shelter in a barn or shed. 

noun
  • The cheese maggot, the larva of a cheese fly (family Piophilidae), which leaps to escape predators. 

  • A barn or shed in which to shelter for the night. 

  • The master of a ship. 

  • A coach, director, or other leader. 

  • One who jumps rope. 

  • Any of various butterflies of the families Hesperiidae and its subfamily Megathyminae, having a hairy mothlike body, hooked tips on the antennae, and a darting flight pattern. 

  • A person who skips, or fails to attend class. 

  • The captain of a sports team such as football, cricket, rugby or curling. 

  • Any of several marine fishes that often leap above water, especially Cololabis saira, the Pacific saury. 

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