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]