The Collaborative International Dictionary of English v.0.48:

Walnut \Wal"nut\, n. [OE. walnot, AS. wealh-hnutu a Welsh or
   foreign nut, a walnut; wealh foreign, strange, n., a
   Welshman, Celt (akin to OHG. Walh, properly, a Celt, from the
   name of a Celtic tribe, in L. Volcae) + hnutu a nut; akin to
   D. walnoot, G. walnuss, Icel. valhnot, Sw. valn["o]t, Dan
   valn["o]d. See Nut, and cf. Welsh.] (Bot.)
   The fruit or nut of any tree of the genus Juglans; also,
   the tree, and its timber. The seven or eight known species
   are all natives of the north temperate zone.
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   Note: In some parts of America, especially in New England,
         the name walnut is given to several species of hickory
         (Carya), and their fruit.
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   Ash-leaved walnut, a tree (Juglans fraxinifolia), native
      in Transcaucasia.

   Black walnut, a North American tree (Juglans nigra)
      valuable for its purplish brown wood, which is extensively
      used in cabinetwork and for gunstocks. The nuts are
      thick-shelled, and nearly globular.

   English walnut, or European walnut, a tree (Juglans
      regia), native of Asia from the Caucasus to Japan,
      valuable for its timber and for its excellent nuts, which
      are also called Madeira nuts.

   Walnut brown, a deep warm brown color, like that of the
      heartwood of the black walnut.

   Walnut oil, oil extracted from walnut meats. It is used in
      cooking, making soap, etc.

   White walnut, a North American tree (Juglans cinerea),
      bearing long, oval, thick-shelled, oily nuts, commonly
      called butternuts. See Butternut.
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The Collaborative International Dictionary of English v.0.48:

Black \Black\ (bl[a^]k), a. [OE. blak, AS. bl[ae]c; akin to
   Icel. blakkr dark, swarthy, Sw. bl[aum]ck ink, Dan. bl[ae]k,
   OHG. blach, LG. & D. blaken to burn with a black smoke. Not
   akin to AS. bl[=a]c, E. bleak pallid. [root]98.]
   1. Destitute of light, or incapable of reflecting it; of the
      color of soot or coal; of the darkest or a very dark
      color, the opposite of white; characterized by such a
      color; as, black cloth; black hair or eyes.
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            O night, with hue so black!           --Shak.
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   2. In a less literal sense: Enveloped or shrouded in
      darkness; very dark or gloomy; as, a black night; the
      heavens black with clouds.
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            I spy a black, suspicious, threatening cloud.
                                                  --Shak.
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   3. Fig.: Dismal, gloomy, or forbidding, like darkness;
      destitute of moral light or goodness; atrociously wicked;
      cruel; mournful; calamitous; horrible. "This day's black
      fate." "Black villainy." "Arise, black vengeance." "Black
      day." "Black despair." --Shak.
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   4. Expressing menace, or discontent; threatening; sullen;
      foreboding; as, to regard one with black looks.
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   Note: Black is often used in self-explaining compound words;
         as, black-eyed, black-faced, black-haired,
         black-visaged.
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   Black act, the English statute 9 George I, which makes it a
      felony to appear armed in any park or warren, etc., or to
      hunt or steal deer, etc., with the face blackened or
      disguised. Subsequent acts inflicting heavy penalties for
      malicious injuries to cattle and machinery have been
      called black acts.

   Black angel (Zool.), a fish of the West Indies and Florida
      (Holacanthus tricolor), with the head and tail yellow,
      and the middle of the body black.

   Black antimony (Chem.), the black sulphide of antimony,
      Sb2S3, used in pyrotechnics, etc.

   Black bear (Zool.), the common American bear (Ursus
      Americanus).

   Black beast. See B[^e]te noire.

   Black beetle (Zool.), the common large cockroach (Blatta
      orientalis).

   Black bonnet (Zool.), the black-headed bunting (Embriza
      Sch[oe]niclus) of Europe.

   Black canker, a disease in turnips and other crops,
      produced by a species of caterpillar.

   Black cat (Zool.), the fisher, a quadruped of North America
      allied to the sable, but larger. See Fisher.

   Black cattle, any bovine cattle reared for slaughter, in
      distinction from dairy cattle. [Eng.]

   Black cherry. See under Cherry.

   Black cockatoo (Zool.), the palm cockatoo. See Cockatoo.


   Black copper. Same as Melaconite.

   Black currant. (Bot.) See Currant.

   Black diamond. (Min.) See Carbonado.

   Black draught (Med.), a cathartic medicine, composed of
      senna and magnesia.

   Black drop (Med.), vinegar of opium; a narcotic preparation
      consisting essentially of a solution of opium in vinegar.


   Black earth, mold; earth of a dark color. --Woodward.

   Black flag, the flag of a pirate, often bearing in white a
      skull and crossbones; a signal of defiance.

   Black flea (Zool.), a flea beetle (Haltica nemorum)
      injurious to turnips.

   Black flux, a mixture of carbonate of potash and charcoal,
      obtained by deflagrating tartar with half its weight of
      niter. --Brande & C.

   Black Forest [a translation of G. Schwarzwald], a forest in
      Baden and W["u]rtemburg, in Germany; a part of the ancient
      Hercynian forest.

   Black game, or Black grouse. (Zool.) See Blackcock,
      Grouse, and Heath grouse.

   Black grass (Bot.), a grasslike rush of the species Juncus
      Gerardi, growing on salt marshes, and making good hay.

   Black gum (Bot.), an American tree, the tupelo or
      pepperidge. See Tupelo.

   Black Hamburg (grape) (Bot.), a sweet and juicy variety of
      dark purple or "black" grape.

   Black horse (Zool.), a fish of the Mississippi valley
      (Cycleptus elongatus), of the sucker family; the
      Missouri sucker.

   Black lemur (Zool.), the Lemurniger of Madagascar; the
      acoumbo of the natives.

   Black list, a list of persons who are for some reason
      thought deserving of censure or punishment; -- esp. a list
      of persons stigmatized as insolvent or untrustworthy, made
      for the protection of tradesmen or employers. See
      Blacklist, v. t.

   Black manganese (Chem.), the black oxide of manganese,
      MnO2.

   Black Maria, the close wagon in which prisoners are carried
      to or from jail.

   Black martin (Zool.), the chimney swift. See Swift.

   Black moss (Bot.), the common so-called long moss of the
      southern United States. See Tillandsia.

   Black oak. See under Oak.

   Black ocher. See Wad.

   Black pigment, a very fine, light carbonaceous substance,
      or lampblack, prepared chiefly for the manufacture of
      printers' ink. It is obtained by burning common coal tar.


   Black plate, sheet iron before it is tinned. --Knight.

   Black quarter, malignant anthrax with engorgement of a
      shoulder or quarter, etc., as of an ox.

   Black rat (Zool.), one of the species of rats (Mus
      rattus), commonly infesting houses.

   Black rent. See Blackmail, n., 3.

   Black rust, a disease of wheat, in which a black, moist
      matter is deposited in the fissures of the grain.

   Black sheep, one in a family or company who is unlike the
      rest, and makes trouble.

   Black silver. (Min.) See under Silver.

   Black and tan, black mixed or spotted with tan color or
      reddish brown; -- used in describing certain breeds of
      dogs.

   Black tea. See under Tea.

   Black tin (Mining), tin ore (cassiterite), when dressed,
      stamped and washed, ready for smelting. It is in the form
      of a black powder, like fine sand. --Knight.

   Black walnut. See under Walnut.

   Black warrior (Zool.), an American hawk (Buteo Harlani).
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   Syn: Dark; murky; pitchy; inky; somber; dusky; gloomy; swart;
        Cimmerian; ebon; atrocious.
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WordNet (r) 3.0 (2006):

black walnut
    n 1: North American walnut tree with hard dark wood and edible
         nut [syn: black walnut, black walnut tree, black
         hickory, Juglans nigra]
    2: American walnut having a very hard and thick woody shell