The Collaborative International Dictionary of English v.0.48:

Codlin \Cod"lin\, Codling \Cod"ling\, n. [Cf. AS. cod[ae]ppel a
   quince.]
   (a) An apple fit to stew or coddle.
   (b) An immature apple.
       [1913 Webster]

             A codling when 't is almost an apple. --Shak.
       [1913 Webster]

   Codling moth (Zool.), a small moth (Carpocapsa
      Pomonella), which in the larval state (known as the apple
      worm) lives in apples, often doing great damage to the
      crop.
      [1913 Webster]

WordNet (r) 3.0 (2006):

codling moth
    n 1: a small grey moth whose larvae live in apples and English
         walnuts [syn: codling moth, codlin moth, Carpocapsa
         pomonella]