Source : Webster's Revised Unabridged Dictionary (1913)

   {Red chalk}. See under {Chalk}.

   {Red copper} (Min.), red oxide of copper; cuprite.

   {Red coral} (Zo["o]l.), the precious coral ({Corallium
      rubrum}). See Illusts. of {Coral} and {Gorgonlacea}.

   {Red cross}. The cross of St. George, the national emblem of
      the English.
   (b) The Geneva cross. See {Geneva convention}, and {Geneva
       cross}, under {Geneva}.

   {Red currant}. (Bot.) See {Currant}.

   {Red deer}. (Zo["o]l.)
   (a) The common stag ({Cervus elaphus}), native of the forests
       of the temperate parts of Europe and Asia. It is very
       similar to the American elk, or wapiti.
   (b) The Virginia deer. See {Deer}.

   {Red duck} (Zo["o]l.), a European reddish brown duck
      ({Fuligula nyroca}); -- called also {ferruginous duck}.

   {Red ebony}. (Bot.) See {Grenadillo}.

   {Red empress} (Zo["o]l.), a butterfly. See {Tortoise shell}.
      

   {Red fir} (Bot.), a coniferous tree ({Pseudotsuga Douglasii})
      found from British Columbia to Texas, and highly valued
      for its durable timber. The name is sometimes given to
      other coniferous trees, as the Norway spruce and the
      American {Abies magnifica} and {A. nobilis}.

   {Red fire}. (Pyrotech.) See {Blue fire}, under {Fire}.

   {Red flag}. See under {Flag}.

   {Red fox} (Zo["o]l.), the common American fox ({Vulpes
      fulvus}), which is usually reddish in color.

   {Red grouse} (Zo["o]l.), the Scotch grouse, or ptarmigan. See
      under {Ptarmigan}.

   {Red gum}, or {Red gum-tree} (Bot.), a name given to eight
      Australian species of {Eucalyptus} ({Eucalyptus
      amygdalina}, {resinifera}, etc.) which yield a reddish gum
      resin. See {Eucalyptus}.

   {Red hand} (Her.), a left hand appaum['e], fingers erect,
      borne on an escutcheon, being the mark of a baronet of the
      United Kingdom of Great Britain and Ireland; -- called
      also {Badge of Ulster}.

   {Red herring}, the common herring dried and smoked.

Flag \Flag\, n. [Cf. LG. & G. flagge, Sw. flagg, Dan. flag, D.
   vlag. See {Flag} to hang loose.]
   1. That which flags or hangs down loosely.

   2. A cloth usually bearing a device or devices and used to
      indicate nationality, party, etc., or to give or ask
      information; -- commonly attached to a staff to be waved
      by the wind; a standard; a banner; an ensign; the colors;
      as, the national flag; a military or a naval flag.

   3. (Zo["o]l.)
      (a) A group of feathers on the lower part of the legs of
          certain hawks, owls, etc.
      (b) A group of elongated wing feathers in certain hawks.
      (c) The bushy tail of a dog, as of a setter.

   {Black flag}. See under {Black}.

   {Flag captain}, {Flag leutenant}, etc., special officers
      attached to the flagship, as aids to the flag officer.

   {Flag officer}, the commander of a fleet or squadron; an
      admiral, or commodore.

   {Flag of truse}, a white flag carried or displayed to an
      enemy, as an invitation to conference, or for the purpose
      of making some communication not hostile.

   {Flag share}, the flag officer's share of prize money.

   {Flag station} (Railroad), a station at which trains do not
      stop unless signaled to do so, by a flag hung out or
      waved.

   {National flag}, a flag of a particular country, on which
      some national emblem or device, is emblazoned.

   {Red flag}, a flag of a red color, displayed as a signal of
      danger or token of defiance; the emblem of anarchists.

   {To dip, the flag}, to mlower it and quickly restore it to
      its place; -- done as a mark of respect.

   {To hang out the white flag}, to ask truce or quarter, or, in
      some cases, to manifest a friendly design by exhibiting a
      white flag.

   {To hang the flag} {half-mast high or half-staff}, to raise
      it only half way to the mast or staff, as a token or sign
      of mourning.

   {To} {strike, or lower}, {the flag}, to haul it down, in
      token of respect, submission, or, in an engagement, of
      surrender.

   {Yellow flag}, the quarantine flag of all nations; also
      carried at a vessel's fore, to denote that an infectious
      disease is on board.

Source : WordNet®

red flag
     n 1: a flag that serves as a warning signal; "we didn't swim at
          the beach because the red flag was up"
     2: the emblem of socialist revolution
     3: something that irritates or demands immediate action; "doing
        that is like waving a red flag in front of a bull"