From 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]
From WordNet (r) 3.0 (2006) :
unseal
v 1: break the seal of; "He unsealed the letter" [ant: seal]