The Collaborative International Dictionary of English v.0.48:

Metal \Met"al\ (? or ?; 277), n. [F. m['e]tal, L. metallum
   metal, mine, Gr. ? mine; cf. Gr. ? to search after. Cf.
   Mettle, Medal.]
   1. (Chem.) An elementary substance, as sodium, calcium, or
      copper, whose oxide or hydroxide has basic rather than
      acid properties, as contrasted with the nonmetals, or
      metalloids. No sharp line can be drawn between the metals
      and nonmetals, and certain elements partake of both acid
      and basic qualities, as chromium, manganese, bismuth, etc.
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   Note: Popularly, the name is applied to certain hard, fusible
         metals, as gold, silver, copper, iron, tin, lead, zinc,
         nickel, etc., and also to the mixed metals, or metallic
         alloys, as brass, bronze, steel, bell metal, etc.
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   2. Ore from which a metal is derived; -- so called by miners.
      --Raymond.
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   3. A mine from which ores are taken. [Obs.]
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            Slaves . . . and persons condemned to metals. --Jer.
                                                  Taylor.
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   4. The substance of which anything is made; material; hence,
      constitutional disposition; character; temper.
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            Not till God make men of some other metal than
            earth.                                --Shak.
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   5. Courage; spirit; mettle. See Mettle. --Shak.
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   Note: The allusion is to the temper of the metal of a sword
         blade. --Skeat.
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   6. The broken stone used in macadamizing roads and ballasting
      railroads.
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   7. The effective power or caliber of guns carried by a vessel
      of war.
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   8. Glass in a state of fusion. --Knight.
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   9. pl. The rails of a railroad. [Eng.]
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   Base metal (Chem.), any one of the metals, as iron, lead,
      etc., which are readily tarnished or oxidized, in contrast
      with the noble metals. In general, a metal of small value,
      as compared with gold or silver.

   Fusible metal (Metal.), a very fusible alloy, usually
      consisting of bismuth with lead, tin, or cadmium.

   Heavy metals (Chem.), the metallic elements not included in
      the groups of the alkalies, alkaline earths, or the
      earths; specifically, the heavy metals, as gold, mercury,
      platinum, lead, silver, etc.

   Light metals (Chem.), the metallic elements of the alkali
      and alkaline earth groups, as sodium, lithium, calcium,
      magnesium, etc.; also, sometimes, the metals of the
      earths, as aluminium.

   Muntz metal, an alloy for sheathing and other purposes,
      consisting of about sixty per cent of copper, and forty of
      zinc. Sometimes a little lead is added. It is named from
      the inventor.

   Prince's metal (Old Chem.), an alloy resembling brass,
      consisting of three parts of copper to one of zinc; --
      also called Prince Rupert's metal.
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The Collaborative International Dictionary of English v.0.48:

Base \Base\ (b[=a]s), a. [OE. bass, F. bas, low, fr. LL. bassus
   thick, fat, short, humble; cf. L. Bassus, a proper name, and
   W. bas shallow. Cf. Bass a part in music.]
   1. Of little, or less than the usual, height; of low growth;
      as, base shrubs. [Archaic] --Shak.
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   2. Low in place or position. [Obs.] --Shak.
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   3. Of humble birth; or low degree; lowly; mean. [Archaic] "A
      peasant and base swain." --Bacon.
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   4. Illegitimate by birth; bastard. [Archaic]
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            Why bastard? wherefore base?          --Shak.
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   5. Of little comparative value, as metal inferior to gold and
      silver, the precious metals.
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   6. Alloyed with inferior metal; debased; as, base coin; base
      bullion.
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   7. Morally low. Hence: Low-minded; unworthy; without dignity
      of sentiment; ignoble; mean; illiberal; menial; as, a base
      fellow; base motives; base occupations. "A cruel act of a
      base and a cowardish mind." --Robynson (More's Utopia).
      "Base ingratitude." --Milton.
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   8. Not classical or correct. "Base Latin." --Fuller.
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   9. Deep or grave in sound; as, the base tone of a violin. [In
      this sense, commonly written bass.]
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   10. (Law) Not held by honorable service; as, a base estate,
       one held by services not honorable; held by villenage.
       Such a tenure is called base, or low, and the tenant, a
       base tenant.
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   Base fee, formerly, an estate held at the will of the lord;
      now, a qualified fee. See note under Fee, n., 4.

   Base metal. See under Metal.
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   Syn: Dishonorable; worthless; ignoble; low-minded; infamous;
        sordid; degraded.

   Usage: Base, Vile, Mean. These words, as expressing
          moral qualities, are here arranged in the order of
          their strength, the strongest being placed first. Base
          marks a high degree of moral turpitude; vile and mean
          denote, in different degrees, the lack of what is
          valuable or worthy of esteem. What is base excites our
          abhorrence; what is vile provokes our disgust or
          indignation; what is mean awakens contempt. Base is
          opposed to high-minded; vile, to noble; mean, to
          liberal or generous. Ingratitude is base; sycophancy
          is vile; undue compliances are mean.
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WordNet (r) 3.0 (2006):

base metal
    n 1: a metal that is common and not considered precious; "lead,
         iron, copper, tin, and zinc are base metals"