Source : Webster's Revised Unabridged Dictionary (1913)

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