The Collaborative International Dictionary of English v.0.48:

Brood \Brood\, a.
   1. Sitting or inclined to sit on eggs.
      [1913 Webster]

   2. Kept for breeding from; as, a brood mare; brood stock;
      having young; as, a brood sow.
      [1913 Webster]

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:

Brood \Brood\ (br[=oo]d), n. [OE. brod, AS. br[=o]d; akin to D.
   broed, OHG. bruot, G. brut, and also to G. br["u]he broth,
   MHG. br["u]eje, and perh. to E. brawn, breath. Cf. Breed,
   v. t.]
   1. The young birds hatched at one time; a hatch; as, a brood
      of chickens.
      [1913 Webster]

            As a hen doth gather her brood under her wings.
                                                  --Luke xiii.
                                                  34.
      [1913 Webster]

            A hen followed by a brood of ducks.   --Spectator.
      [1913 Webster]

   2. The young from the same dam, whether produced at the same
      time or not; young children of the same mother, especially
      if nearly of the same age; offspring; progeny; as, a woman
      with a brood of children.
      [1913 Webster]

            The lion roars and gluts his tawny brood.
                                                  --Wordsworth.
      [1913 Webster]

   3. That which is bred or produced; breed; species.
      [1913 Webster]

            Flocks of the airy brood,
            (Cranes, geese or long-necked swans). --Chapman.
      [1913 Webster]

   4. (Mining) Heavy waste in tin and copper ores.
      [1913 Webster]

   To sit on brood, to ponder. [Poetic] --Shak.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Brood \Brood\ (br[=oo]d), v. t.
   1. To sit over, cover, and cherish; as, a hen broods her
      chickens.
      [1913 Webster]

   2. To cherish with care. [R.]
      [1913 Webster]

   3. To think anxiously or moodily upon.
      [1913 Webster]

            You'll sit and brood your sorrows on a throne.
                                                  --Dryden.
      [1913 Webster]

WordNet (r) 3.0 (2006):

brood
    n 1: the young of an animal cared for at one time
    v 1: think moodily or anxiously about something [syn: brood,
         dwell]
    2: hang over, as of something threatening, dark, or menacing;
       "The terrible vision brooded over her all day long" [syn:
       brood, hover, loom, bulk large]
    3: be in a huff and display one's displeasure; "She is pouting
       because she didn't get what she wanted" [syn: sulk, pout,
       brood]
    4: be in a huff; be silent or sullen [syn: grizzle, brood,
       stew]
    5: sit on (eggs); "Birds brood"; "The female covers the eggs"
       [syn: brood, hatch, cover, incubate]

Moby Thesaurus II by Grady Ward, 1.0:

114 Moby Thesaurus words for "brood":
   agonize, animal kingdom, be abstracted, be gravid, be knocked up,
   be pregnant, be with child, blood, breed, carry, carry young,
   chew the cud, children, clan, class, clock, clutch, consider,
   contemplate, cover, debate, deliberate, deme, descendants, descent,
   despair, despond, digest, family, farrow, folk, folks, fret, fruit,
   fry, gens, gestate, get, grandchildren, great-grandchildren, hatch,
   hearth, heirs, homefolks, hostages to fortune, house, household,
   incubate, inheritors, introspect, issue, kids, kind, line, lineage,
   litter, little ones, matriclan, meditate, menage, mope, muse,
   muse on, muse over, nation, nest, new generation, offspring, order,
   patriclan, people, perpend, phratry, phyle, pine, plant kingdom,
   play around with, play with, ponder, ponder over, posterity, pout,
   progeniture, progeny, race, reflect, rising generation, ruminate,
   ruminate over, seed, sept, set, sit, sons, spat, spawn, species,
   speculate, stem, stirps, stock, strain, study, succession, sulk,
   totem, toy with, treasures, tribe, weigh, worry, young, younglings,
   youngsters