Source : Webster's Revised Unabridged Dictionary (1913)

Unseal \Un*seal"\, v. t. [1st pref. un- + seal.]
   1. To break or remove the seal of; to open, as what is
      sealed; as, to unseal a letter.

            Unable to unseal his lips beyond the width of a
            quarter of an inch.                   --Sir W.
                                                  Scott.

   2. To disclose, as a secret. [Obs.] --The Coronation.

Source : WordNet®

unseal
     v : break the seal of; "He unsealed the letter" [ant: {seal}]