Adirondack (adj.) Look up Adirondack at Dictionary.com
1906 in reference to a type of lawn or deck chair said to have been designed in 1903 by a Thomas Lee, owner of the Westport Mountain Spring, a resort in the Adirondack region of New York State, and commercially manufactured the following year, but said originally to have been called Westport chair after the town where it was first made.

Adirondack Mountains is a back-formation from Adirondacks, which was treated as a plural noun but really it is from Mohawk (Iroquoian) adiro:daks "tree-eaters," a name they applied to neighboring Algonquian tribes. The -s is an imperfective affix.