The Collaborative International Dictionary of English v.0.48:

Brass \Brass\, n.; pl. Brasses. [OE. bras, bres, AS. br[ae]s;
   akin to Icel. bras cement, solder, brasa to harden by fire,
   and to E. braze, brazen. Cf. 1st & 2d Braze.]
   1. An alloy (usually yellow) of copper and zinc, in variable
      proportion, but often containing two parts of copper to
      one part of zinc. It sometimes contains tin, and rarely
      other metals.
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   2. (Mach.) A journal bearing, so called because frequently
      made of brass. A brass is often lined with a softer metal,
      when the latter is generally called a white metal lining.
      See Axle box, Journal Box, and Bearing.
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   3. Coin made of copper, brass, or bronze. [Obs.]
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            Provide neither gold, nor silver, nor brass in your
            purses, nor scrip for your journey.   --Matt. x. 9.
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   4. Impudence; a brazen face. [Colloq.]
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   5. pl. Utensils, ornaments, or other articles of brass.
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            The very scullion who cleans the brasses.
                                                  --Hopkinson.
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   6. A brass plate engraved with a figure or device.
      Specifically, one used as a memorial to the dead, and
      generally having the portrait, coat of arms, etc.
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   7. pl. (Mining) Lumps of pyrites or sulphuret of iron, the
      color of which is near to that of brass.
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   Note: The word brass as used in Sculpture language is a
         translation for copper or some kind of bronze.
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   Note: Brass is often used adjectively or in self-explaining
         compounds; as, brass button, brass kettle, brass
         founder, brass foundry or brassfoundry.
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   Brass band (Mus.), a band of musicians who play upon wind
      instruments made of brass, as trumpets, cornets, etc.

   Brass foil, Brass leaf, brass made into very thin sheets;
      -- called also Dutch gold.
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WordNet (r) 3.0 (2006):

brass band
    n 1: a group of musicians playing only brass and percussion
         instruments