harbor vs harbour

harbor

verb
  • To provide a harbor or safe place for. 

  • To take refuge or shelter in a protected expanse of water. 

  • To drive (a hunted stag) to covert. 

  • To hold or persistently entertain in one's thoughts or mind. 

noun
  • A sheltered expanse of water, adjacent to land, in which ships may anchor or dock, especially for loading and unloading. 

  • Any place of shelter. 

  • A mixing box for materials. 

  • A harbor, even if it is a little harbor, is a good thing, since adventurers come into it as well as go out, and the life in it grows strong, because it takes something from the world, and has something to give in return - Sarah Orne Jewett 

harbour

verb
  • Commonwealth standard spelling of harbor. 

noun
  • Commonwealth standard spelling of harbor. 

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