The Collaborative International Dictionary of English v.0.48:

Darn \Darn\ (d[aum]rn), v. t. [imp. & p. p. Darned
   (d[aum]rnd); p. pr. & vb. n. Darning.] [OE. derne, prob. of
   Celtic origin; cf. W. darnio to piece, break in pieces, W. &
   Arm. to E. tear. Cf. Tear, v. t.]
   To mend as a rent or hole, with interlacing stitches of yarn
   or thread by means of a needle; to sew together with yarn or
   thread.
   [1913 Webster]

         He spent every day ten hours in his closet, in darning
         his stockings.                           --Swift.
   [1913 Webster]

   Darning last. See under Last.

   Darning needle.
   (a) A long, strong needle for mending holes or rents,
       especially in stockings.
   (b) (Zool.) Any species of dragon fly, having a long,
       cylindrical body, resembling a needle. These flies are
       harmless and without stings.

   Note: [In this sense, usually written with a hyphen.] Called
         also devil's darning-needle.
         [1913 Webster]

WordNet (r) 3.0 (2006):

darning
    n 1: the act of mending a hole in a garment with crossing
         threads