The Collaborative International Dictionary of English v.0.48:

Longing \Long"ing\, n.
   An eager desire; a craving; a morbid appetite; an earnest
   wish; an aspiration.
   [1913 Webster]

         Put on my crown; I have
         immortal longings in me.                 --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Long \Long\, v. i. [imp. & p. p. Longed; p. pr. & vb. n.
   Longing.] [AS. langian to increase, to lengthen, to stretch
   out the mind after, to long, to crave, to belong to, fr. lang
   long. See Long, a.]
   1. To feel a strong or morbid desire or craving; to wish for
      something with eagerness; -- followed by an infinitive, or
      by for or after.
      [1913 Webster]

            I long to see you.                    --Rom. i. 11.
      [1913 Webster]

            I have longed after thy precepts.     --Ps. cxix.
                                                  40.
      [1913 Webster]

            I have longed for thy salvation.      --Ps. cxix.
                                                  174.
      [1913 Webster]

            Nicomedes, longing for herrings, was supplied with
            fresh ones . . . at a great distance from the sea.
                                                  --Arbuthnot.
      [1913 Webster]

   2. To belong; -- used with to, unto, or for. [Obs.]
      [1913 Webster]

            The labor which that longeth unto me. --Chaucer.
      [1913 Webster]

WordNet (r) 3.0 (2006):

longing
    n 1: prolonged unfulfilled desire or need [syn: longing,
         yearning, hungriness]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "longing":
   Heimweh, aching, craving, desiderium, desire, fancy, hankering,
   homesick, homesickness, honing, hunger, languishing, languishment,
   mal du pays, maladie du pays, nostalgia, nostalgic, nostomania,
   pining, wish, wishful, wistful, yearnful, yearning, yen