Wordnet 3.0
VERB (1)
1. 
 break the seal of; 
- Example: "He unsealed the letter"
The Collaborative International Dictionary of English v.0.48:
Unseal \Un*seal"\ ([u^]n*s[=e]l"), 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.
      [1913 Webster]
            Unable to unseal his lips beyond the width of a
            quarter of an inch.                   --Sir W.
                                                  Scott.
      [1913 Webster]
   2. To disclose, as a secret. [Obs.] --The Coronation.
      [1913 Webster]
WordNet (r) 3.0 (2006):
unseal
    v 1: break the seal of; "He unsealed the letter" [ant: seal]