Source : Webster's Revised Unabridged Dictionary (1913)

Pumpernickel \Pump"er*nick`el\, n. [G.]
   A sort of bread, made of unbolted rye, which forms the chief
   food of the Westphalian peasants. It is acid but nourishing.

Source : WordNet®

pumpernickel
     n : bread made of coarse rye flour [syn: {black bread}]