The Collaborative International Dictionary of English v.0.48:

Dunkirk \Dunkirk\ prop. n.
   the name of a town and a battle fought there, in World War II
   (1940) when 330,000 Allied troops had to be evacuated from
   the beaches at Dunkirk in a desperate retreat under enemy
   fire. Most of the forces were safely evacuated to England.

   Syn: Dunkerque.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Dunkirk
    n 1: a crisis in which a desperate effort is the only
         alternative to defeat; "the Russians had to pull off a
         Dunkirk to get out of there"
    2: a seaport in northern France on the North Sea; scene of the
       evacuation of British forces in 1940 during World War II
       [syn: Dunkirk, Dunkerque]
    3: an amphibious evacuation in World War II (1940) when 330,000
       Allied troops had to be evacuated from the beaches in
       northern France in a desperate retreat under enemy fire [syn:
       Dunkirk, Dunkerque]