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Webster 1913 Edition

Verb.

[1st pref.

un-

pen

To release from a pen or from confinement.

“If a man unpens another’s water.”

Blackstone.

Verb.

To let out or suffer to escape by breaking a dam or opening a pen.

If a man unpens another's water -

unpen ‎(third-person singular simple present unpens, present participle unpenning, simple past and past participle unpenned)