The Collaborative International Dictionary of English v.0.48:

Mail \Mail\ (m[=a]l), n. [OE. maile, maille, F. maille a ring of
   mail, mesh, network, a coat of mail, fr. L. macula spot, a
   mesh of a net. Cf. Macle, Macula, Mascle.]
   1. A flexible fabric made of metal rings interlinked. It was
      used especially for defensive armor. --Chaucer.
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   Chain mail, Coat of mail. See under Chain, and Coat.
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   2. Hence generally, armor, or any defensive covering.
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   3. (Naut.) A contrivance of interlinked rings, for rubbing
      off the loose hemp on lines and white cordage.
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   4. (Zool.) Any hard protective covering of an animal, as the
      scales and plates of reptiles, shell of a lobster, etc.
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            We . . . strip the lobster of his scarlet mail.
                                                  --Gay.
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The Collaborative International Dictionary of English v.0.48:

Chain \Chain\ (ch[=a]n), n. [F. cha[^i]ne, fr. L. catena. Cf.
   Catenate.]
   1. A series of links or rings, usually of metal, connected,
      or fitted into one another, used for various purposes, as
      of support, of restraint, of ornament, of the exertion and
      transmission of mechanical power, etc.
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            [They] put a chain of gold about his neck. --Dan. v.
                                                  29.
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   2. That which confines, fetters, or secures, as a chain; a
      bond; as, the chains of habit.
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            Driven down
            To chains of darkness and the undying worm.
                                                  --Milton.
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   3. A series of things linked together; or a series of things
      connected and following each other in succession; as, a
      chain of mountains; a chain of events or ideas.
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   4. (Surv.) An instrument which consists of links and is used
      in measuring land.
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   Note: One commonly in use is Gunter's chain, which consists
         of one hundred links, each link being seven inches and
         ninety-two one hundredths in length; making up the
         total length of rods, or sixty-six, feet; hence, a
         measure of that length; hence, also, a unit for land
         measure equal to four rods square, or one tenth of an
         acre.
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   5. pl. (Naut.) Iron links bolted to the side of a vessel to
      bold the dead-eyes connected with the shrouds; also, the
      channels.
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   6. (Weaving) The warp threads of a web. --Knight.
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   Chain belt (Mach.), a belt made of a chain; -- used for
      transmitting power.

   Chain boat, a boat fitted up for recovering lost cables,
      anchors, etc.

   Chain bolt
      (a) (Naut.) The bolt at the lower end of the chain plate,
          which fastens it to the vessel's side.
      (b) A bolt with a chain attached for drawing it out of
          position.

   Chain bond. See Chain timber.

   Chain bridge, a bridge supported by chain cables; a
      suspension bridge.

   Chain cable, a cable made of iron links.

   Chain coral (Zool.), a fossil coral of the genus
      Halysites, common in the middle and upper Silurian
      rocks. The tubular corallites are united side by side in
      groups, looking in an end view like links of a chain. When
      perfect, the calicles show twelve septa.

   Chain coupling.
      (a) A shackle for uniting lengths of chain, or connecting
          a chain with an object.
      (b) (Railroad) Supplementary coupling together of cars
          with a chain.

   Chain gang, a gang of convicts chained together.

   Chain hook (Naut.), a hook, used for dragging cables about
      the deck.

   Chain mail, flexible, defensive armor of hammered metal
      links wrought into the form of a garment.

   Chain molding (Arch.), a form of molding in imitation of a
      chain, used in the Normal style.

   Chain pier, a pier suspended by chain.

   Chain pipe (Naut.), an opening in the deck, lined with
      iron, through which the cable is passed into the lockers
      or tiers.

   Chain plate (Shipbuilding), one of the iron plates or
      bands, on a vessel's side, to which the standing rigging
      is fastened.

   Chain pulley, a pulley with depressions in the periphery of
      its wheel, or projections from it, made to fit the links
      of a chain.

   Chain pumps. See in the Vocabulary.

   Chain rule (Arith.), a theorem for solving numerical
      problems by composition of ratios, or compound proportion,
      by which, when several ratios of equality are given, the
      consequent of each being the same as the antecedent of the
      next, the relation between the first antecedent and the
      last consequent is discovered.

   Chain shot (Mil.), two cannon balls united by a shot chain,
      formerly used in naval warfare on account of their
      destructive effect on a ship's rigging.

   Chain stitch. See in the Vocabulary.

   Chain timber. (Arch.) See Bond timber, under Bond.

   Chain wales. (Naut.) Same as Channels.

   Chain wheel. See in the Vocabulary.

   Closed chain, Open chain (Chem.), terms applied to the
      chemical structure of compounds whose rational formul[ae]
      are written respectively in the form of a closed ring (see
      Benzene nucleus, under Benzene), or in an open
      extended form.

   Endless chain, a chain whose ends have been united by a
      link.
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WordNet (r) 3.0 (2006):

chain mail
    n 1: (Middle Ages) flexible armor made of interlinked metal
         rings [syn: chain mail, ring mail, mail, chain
         armor, chain armour, ring armor, ring armour]