WordNet (r) 3.0 (2006):

iron curtain
    n 1: an impenetrable barrier to communication or information
         especially as imposed by rigid censorship and secrecy; used
         by Winston Churchill in 1946 to describe the demarcation
         between democratic and communist countries

Moby Thesaurus II by Grady Ward, 1.0:

96 Moby Thesaurus words for "iron curtain":
   Berlin wall, Bolshevism, Castroism, Communist Information Bureau,
   Communist Party, Maoism, Marxian socialism, Marxism,
   Marxism-Leninism, Pillars of Hercules, Stalinism, Titoism,
   Trotskyism, arch dam, backstop, bamboo curtain, bank, bar, barrage,
   barrier, barrier of secrecy, bear-trap dam, beaver dam, blackout,
   boom, border, border ground, borderland, breakwater, breastwork,
   brick wall, buffer, bulkhead, bulwark, censorship, cofferdam,
   communism, curtain, dam, defense, democratic centralism,
   dialectical materialism, dike, ditch, earthwork, embankment, fence,
   frontier, frontier post, gate, gravity dam, groin, hush-up,
   hydraulic-fill dam, ironbound security, jam, jetty, leaping weir,
   levee, logjam, march, marches, marchland, milldam, moat, mole,
   mound, oath of secrecy, official secrecy, outpost, outskirts, pall,
   parapet, portcullis, rampart, repression, revisionism, roadblock,
   rock-fill dam, seal of secrecy, seawall, security, shutter dam,
   smothering, stifling, stone wall, suppression, three-mile limit,
   twelve-mile limit, veil, veil of secrecy, wall, weir, wicket dam,
   work, wraps