The Collaborative International Dictionary of English v.0.48:

Corny \Cor"ny\ (k?r"n?), a. [L. cornu horn.]
   Strong, stiff, or hard, like a horn; resembling horn.
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         Up stood the cornu reed.                 --Milton.
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The Collaborative International Dictionary of English v.0.48:

Corny \Corn"y\, a.
   1. Producing corn or grain; furnished with grains of corn.
      [R.] "The corny ear." --Prior.
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   2. Containing corn; tasting well of malt. [R.]
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            A draught of moist and corny ale.     --Chaucer.
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   3. Tipsy. [Vulgar, Eng.] --Forby.
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   4. overly or simplistically sentimental. [informal]
      [PJC]

   5. trite or tiresome; too weak to be effective; -- said of
      unsubtle attempts at humor; as, a corny joke; a corny
      skit. [informal]
      [PJC]

WordNet (r) 3.0 (2006):

corny
    adj 1: dull and tiresome but with pretensions of significance or
           originality; "bromidic sermons" [syn: bromidic,
           corny, platitudinal, platitudinous]