Source : Webster's Revised Unabridged Dictionary (1913)

Imprimatur \Im`pri*ma"tur\, n. [L., let it be printed.] (Law)
   A license to print or publish a book, paper, etc.; also, in
   countries subjected to the censorship of the press, approval
   of that which is published.

Source : WordNet®

imprimatur
     n : formal and explicit approval; "a Democrat usually gets the
         union's endorsement" [syn: {sanction}, {countenance}, {endorsement},
          {indorsement}, {warrant}]