The Collaborative International Dictionary of English v.0.48:

Thule \Thu"le\ (th[=u]"l[-e]), prop. n. [L. Thule, Thyle, Gr.
   Qoy`lh, Qy`lh.]
   The name given by ancient geographers to the northernmost
   part of the habitable world. According to some, this land was
   Norway, according to others, Iceland, or more probably
   Mainland, the largest of the Shetland islands; hence, the
   Latin phrase ultima Thule, farthest Thule.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Thule
    n 1: a town in northwestern Greenland; during World War II a
         United States naval base was built there
    2: the geographical region believed by ancient geographers to be
       the northernmost land in the inhabited world [syn: Thule,
       ultima Thule]