The Collaborative International Dictionary of English v.0.48:

Chinook \Chi*nook"\, n.
   1. (Ethnol.) One of a tribe of North American Indians now
      living in the state of Washington, noted for the custom of
      flattening their skulls. Chinooks also called Flathead
      Indians.
      [1913 Webster]

   2. A warm westerly wind from the country of the Chinooks,
      sometimes experienced on the slope of the Rocky Mountains,
      in Montana and the adjacent territory.
      [1913 Webster]

   3. A jargon of words from various languages (the largest
      proportion of which is from that of the Chinooks)
      generally understood by all the Indian tribes of the
      northwestern territories of the United States.
      [1913 Webster]