Source : Webster's Revised Unabridged Dictionary (1913)

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.

            Birds of calm sir brooding on the charmed wave.
                                                  --Milton.

   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.

            Brooding on unprofitable gold.        --Dryden.

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

            When with downcast eyes we muse and brood.
                                                  --Tennyson.

Source : WordNet®

brooding
     adj : persistently or morbidly thoughtful [syn: {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: {incubation}]
     2: persistent morbid meditation on a problem [syn: {pensiveness}]