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
    n 1: an alloy of copper and zinc
    2: a wind instrument that consists of a brass tube (usually of
       variable length) that is blown by means of a cup-shaped or
       funnel-shaped mouthpiece [syn: brass, brass instrument]
    3: the persons (or committees or departments etc.) who make up a
       body for the purpose of administering something; "he claims
       that the present administration is corrupt"; "the governance
       of an association is responsible to its members"; "he quickly
       became recognized as a member of the establishment" [syn:
       administration, governance, governing body,
       establishment, brass, organization, organisation]
    4: impudent aggressiveness; "I couldn't believe her boldness";
       "he had the effrontery to question my honesty" [syn:
       boldness, nerve, brass, face, cheek]
    5: an ornament or utensil made of brass
    6: the section of a band or orchestra that plays brass
       instruments [syn: brass section, brass]
    7: a memorial made of brass [syn: brass, memorial tablet,
       plaque]