The Collaborative International Dictionary of English v.0.48:

Unlearn \Un*learn"\, v. t. [1st pref. un- + learn.]
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   1. To forget, as what has been learned; to lose from memory;
      also, to learn the contrary of.
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            I had learned nothing right; I had to unlearn
            everything.                           --Milner.
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   2. To fail to learn. [Obs.] --Dr. H. More.
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