The Collaborative International Dictionary of English v.0.48:

Monkey's puzzle \Mon"key's puz"zle\ (Bot.)
   A lofty coniferous Chilian tree (Araucaria araucana,
   formerly Araucaria imbricata), the branches of which are so
   crowded and intertwisted "as to puzzle a monkey to climb." It
   is also called monkey puzzle and monkey puzzle tree. The
   edible nuts are over an inch long, and are called pi[~n]on by
   the Chilians.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Araucaria araucana
    n 1: large Chilean evergreen conifer having intertwined branches
         and bearing edible nuts [syn: monkey puzzle, chile
         pine, Araucaria araucana]