Source : Webster's Revised Unabridged Dictionary (1913)

Pigeonhole \Pi"geon*hole`\, n.
   A small compartment in a desk or case for the keeping of
   letters, documents, etc.; -- so called from the resemblance
   of a row of them to the compartments in a dovecote. --Burke.

Pigeonhole \Pi"geon*hole`\, v. t.
   To place in the pigeonhole of a case or cabinet; hence, to
   put away; to lay aside indefinitely; as, to pigeonhole a
   letter or a report.

Source : WordNet®

pigeonhole
     n 1: a specific (often simplistic) category
     2: a small compartment [syn: {cubbyhole}]
     v 1: place into a small compartment
     2: treat or classify according to a mental stereotype; "I was
        stereotyped as a lazy Southern European" [syn: {stereotype},
         {stamp}]