The Collaborative International Dictionary of English v.0.48:

Brood \Brood\, a.
   1. Sitting or inclined to sit on eggs.
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   2. Kept for breeding from; as, a brood mare; brood stock;
      having young; as, a brood sow.
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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.
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            Birds of calm sir brooding on the charmed wave.
                                                  --Milton.
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   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.
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            Brooding on unprofitable gold.        --Dryden.
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            Brooding over all these matters, the mother felt
            like one who has evoked a spirit.     --Hawthorne.
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            When with downcast eyes we muse and brood.
                                                  --Tennyson.
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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.
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            As a hen doth gather her brood under her wings.
                                                  --Luke xiii.
                                                  34.
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            A hen followed by a brood of ducks.   --Spectator.
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   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.
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            The lion roars and gluts his tawny brood.
                                                  --Wordsworth.
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   3. That which is bred or produced; breed; species.
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            Flocks of the airy brood,
            (Cranes, geese or long-necked swans). --Chapman.
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   4. (Mining) Heavy waste in tin and copper ores.
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   To sit on brood, to ponder. [Poetic] --Shak.
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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.
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   2. To cherish with care. [R.]
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   3. To think anxiously or moodily upon.
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            You'll sit and brood your sorrows on a throne.
                                                  --Dryden.
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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]