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:

Coat \Coat\ (k[=o]t; 110), n. [OF. cote, F. cotte, petticoat,
   cotte d'armes coat of arms, cotte de mailles coat of mail,
   LL. cota, cotta, tunic, prob. of German origin; cf. OHG.
   chozzo coarse mantle, G. klotze, D. kot, hut, E. cot. Cf.
   Cot a hut.]
   1. An outer garment fitting the upper part of the body;
      especially, such a garment worn by men.
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            Let each
            His adamantine coat gird well.        --Milton.
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   2. A petticoat. [Obs.] "A child in coats." --Locke.
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   3. The habit or vesture of an order of men, indicating the
      order or office; cloth.
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            Men of his coat should be minding their prayers.
                                                  --Swift.
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            She was sought by spirits of richest coat. --Shak.
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   4. An external covering like a garment, as fur, skin, wool,
      husk, or bark; as, the horses coats were sleek.
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            Fruit of all kinds, in coat
            Rough or smooth rined, or bearded husk, or shell.
                                                  --Milton.
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   5. A layer of any substance covering another; a cover; a
      tegument; as, the coats of the eye; the coats of an onion;
      a coat of tar or varnish.
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   6. Same as Coat of arms. See below.
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            Hark, countrymen! either renew the fight,
            Or tear the lions out of England's coat. --Shak.
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   7. A coat card. See below. [Obs.]
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            Here's a trick of discarded cards of us! We were
            ranked with coats as long as old master lived.
                                                  --Massinger.
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   Coat armor. See under Armor.

   Coat of arms (Her.), a translation of the French cotte
      d'armes, a garment of light material worn over the armor
      in the 15th and 16th centuries. This was often charged
      with the heraldic bearings of the wearer. Hence, an
      heraldic achievement; the bearings of any person, taken
      together.

   Coat card, a card bearing a coated figure; the king, queen,
      or knave of playing cards. "`I am a coat card indeed.'
      `Then thou must needs be a knave, for thou art neither
      king nor queen.'" --Rowley.

   Coat link, a pair of buttons or studs joined by a link, to
      hold together the lappels of a double-breasted coat; or a
      button with a loop for a single-breasted coat.

   Coat of mail, a defensive garment of chain mail. See Chain
      mail, under Chain.

   Mast coat (Naut.), a piece of canvas nailed around a mast,
      where it passes through the deck, to prevent water from
      getting below.

   Sail coat (Naut.), a canvas cover laced over furled sails,
      and the like, to keep them dry and clean.
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WordNet (r) 3.0 (2006):

coat of mail
    n 1: armor that protects the wearer's whole body [syn: body
         armor, body armour, suit of armor, suit of armour,
         coat of mail, cataphract]

Easton's 1897 Bible Dictionary:

Coat of mail
   the rendering of a Hebrew word meaning "glittering" (1 Sam.
   17:5, 38). The same word in the plural form is translated
   "habergeons" in 2 Chr. 26:14 and Neh. 4:16. The "harness" (1
   Kings 22:34), "breastplate" (Isa. 59:17), and "brigandine" (Jer.
   46:4), were probably also corselets or coats of mail. (See ARMOUR.)