Wordnet 3.0
NOUN (1)
1. 
 the secrecy of police officers who lie or look the other way to protect other police officers; 
- Example: "the blue wall cracked when some officers refused to take part in the cover-up"[syn: blue wall of silence, blue wall, wall of silence]
WordNet (r) 3.0 (2006):
wall of silence
    n 1: the secrecy of police officers who lie or look the other
         way to protect other police officers; "the blue wall
         cracked when some officers refused to take part in the
         cover-up" [syn: blue wall of silence, blue wall, wall
         of silence]