The Collaborative International Dictionary of English v.0.48:

Brood \Brood\ (br[=o]ch), v. i. [imp. & p. p. Brooded; p. pr.
   & vb. n. Brooding.]
   1. To sit on and cover eggs, as a fowl, for the purpose of
      warming them and hatching the young; or to sit over and
      cover young, as a hen her chickens, in order to warm and
      protect them; hence, to sit quietly, as if brooding.
      [1913 Webster]

            Birds of calm sir brooding on the charmed wave.
                                                  --Milton.
      [1913 Webster]

   2. To have the mind dwell continuously or moodily on a
      subject; to think long and anxiously; to be in a state of
      gloomy, serious thought; -- usually followed by over or
      on; as, to brood over misfortunes.
      [1913 Webster]

            Brooding on unprofitable gold.        --Dryden.
      [1913 Webster]

            Brooding over all these matters, the mother felt
            like one who has evoked a spirit.     --Hawthorne.
      [1913 Webster]

            When with downcast eyes we muse and brood.
                                                  --Tennyson.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

brooding \brood"ing\, a.
   1. worried and thinking long and intensely, especially about
      a particular problem.

   Syn: broody, contemplative, meditative, musing, pensive,
        pondering, reflective, ruminative, gloomy, morose.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

brooding \brood"ing\, a.
   good at incubating eggs, especially of a fowl kept for that
   purpose; as, a brooding hen.

   Syn: brood, hatching.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

brooding \brooding\ n.
   the process of sitting on eggs so as to hatch them by the
   warmth of the body; -- mostly used of birds.

   Syn: incubation.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

brooding
    adj 1: deeply or seriously thoughtful; "Byron lives on not only
           in his poetry, but also in his creation of the 'Byronic
           hero' - the persona of a brooding melancholy young man";
           [syn: brooding, broody, contemplative,
           meditative, musing, pensive, pondering,
           reflective, ruminative]
    n 1: sitting on eggs so as to hatch them by the warmth of the
         body [syn: brooding, incubation]
    2: persistent morbid meditation on a problem [syn:
       pensiveness, brooding]