unpen

from The Collaborative International Dictionary of English v.0.48

Unpen \Un*pen"\, v. t. [1st pref. un- + pen.]
   To release from a pen or from confinement. "If a man unpens
   another's water." --Blackstone.
   [1913 Webster]

from Moby Thesaurus II by Grady Ward, 1.0

28 Moby Thesaurus words for "unpen":
      loose, loosen, unbar, unbind, unbolt, unbridle, unbuckle, uncage,
      unchain, unfetter, ungag, unhandcuff, unhobble, unlash, unlatch,
      unleash, unlock, unloose, unloosen, unmanacle, unmuzzle, unpinion,
      unshackle, unstrap, untether, untie, untruss, unyoke

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