What is Na-dene?

Na-dene definition and meaning on Dictionary terms:

a group of North American Indian languages, comprising the Athabaskan family, Eyak, Tlingit, and Haida, hypothetically considered to be descendants of a single protolanguage: the genetic relationship of either Tlingit or Haida to Athabaskan and Eyak is now disputed.
the hypothesized protolanguage itself.