The Collaborative International Dictionary of English v.0.48:

Vitriol \Vit"ri*ol\, n. [F. vitriol; cf. Pr. vitriol, vetriol,
   Sp. & Pg. vitriolo, It. vitriuolo; fr. L. vitreolus of glass,
   vitreus vitreous. See Vitreous.] (Chem.)
   (a) A sulphate of any one of certain metals, as copper, iron,
       zinc, cobalt. So called on account of the glassy
       appearance or luster.
   (b) Sulphuric acid; -- called also oil of vitriol. So
       called because first made by the distillation of green
       vitriol. See Sulphuric acid, under Sulphuric.
       [Colloq.]
       [1913 Webster]

   Blue vitriol. See under Blue.

   Green vitriol, ferrous sulphate; copperas. See under
      Green.

   Oil of vitriol, sulphuric or vitriolic acid; -- popularly
      so called because it has the consistency of oil.

   Red vitriol, a native sulphate of cobalt.

   Vitriol of Mars, ferric sulphate, a white crystalline
      substance which dissolves in water, forming a red
      solution.

   White vitriol, zinc sulphate, a white crystalline substance
      used in medicine and in dyeing. It is usually obtained by
      dissolving zinc in sulphuric acid, or by roasting and
      oxidizing certain zinc ores. Formerly called also vitriol
      of zinc.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Blue \Blue\ (bl[=u]), a. [Compar. Bluer (bl[=u]"[~e]r);
   superl. Bluest.] [OE. bla, blo, blew, blue, livid, black,
   fr. Icel.bl[=a]r livid; akin to Dan. blaa blue, Sw. bl[*a],
   D. blauw, OHG. bl[=a]o, G. blau; but influenced in form by F.
   bleu, from OHG. bl[=a]o.]
   1. Having the color of the clear sky, or a hue resembling it,
      whether lighter or darker; as, the deep, blue sea; as blue
      as a sapphire; blue violets. "The blue firmament."
      --Milton.
      [1913 Webster]

   2. Pale, without redness or glare, -- said of a flame; hence,
      of the color of burning brimstone, betokening the presence
      of ghosts or devils; as, the candle burns blue; the air
      was blue with oaths.
      [1913 Webster]

   3. Low in spirits; melancholy; as, to feel blue.
      [1913 Webster]

   4. Suited to produce low spirits; gloomy in prospect; as,
      thongs looked blue. [Colloq.]
      [1913 Webster]

   5. Severe or over strict in morals; gloom; as, blue and sour
      religionists; suiting one who is over strict in morals;
      inculcating an impracticable, severe, or gloomy mortality;
      as, blue laws.
      [1913 Webster]

   6. Literary; -- applied to women; -- an abbreviation of
      bluestocking. [Colloq.]
      [1913 Webster]

            The ladies were very blue and well informed.
                                                  --Thackeray.
      [1913 Webster]

   Blue asbestus. See Crocidolite.

   Blue black, of, or having, a very dark blue color, almost
      black.

   Blue blood. See under Blood.

   Blue buck (Zool.), a small South African antelope
      (Cephalophus pygm[ae]us); also applied to a larger
      species ([AE]goceras leucoph[ae]us); the blaubok.

   Blue cod (Zool.), the buffalo cod.

   Blue crab (Zool.), the common edible crab of the Atlantic
      coast of the United States (Callinectes hastatus).

   Blue curls (Bot.), a common plant (Trichostema
      dichotomum), resembling pennyroyal, and hence called also
      bastard pennyroyal.

   Blue devils, apparitions supposed to be seen by persons
      suffering with delirium tremens; hence, very low
      spirits. "Can Gumbo shut the hall door upon blue devils,
      or lay them all in a red sea of claret?" --Thackeray.

   Blue gage. See under Gage, a plum.

   Blue gum, an Australian myrtaceous tree (Eucalyptus
      globulus), of the loftiest proportions, now cultivated in
      tropical and warm temperate regions for its timber, and as
      a protection against malaria. The essential oil is
      beginning to be used in medicine. The timber is very
      useful. See Eucalyptus.

   Blue jack, Blue stone, blue vitriol; sulphate of copper.


   Blue jacket, a man-of war's man; a sailor wearing a naval
      uniform.

   Blue jaundice. See under Jaundice.

   Blue laws, a name first used in the eighteenth century to
      describe certain supposititious laws of extreme rigor
      reported to have been enacted in New Haven; hence, any
      puritanical laws. [U. S.]

   Blue light, a composition which burns with a brilliant blue
      flame; -- used in pyrotechnics and as a night signal at
      sea, and in military operations.

   Blue mantle (Her.), one of the four pursuivants of the
      English college of arms; -- so called from the color of
      his official robes.

   Blue mass, a preparation of mercury from which is formed
      the blue pill. --McElrath.

   Blue mold or Blue mould, the blue fungus (Aspergillus
      glaucus) which grows on cheese. --Brande & C.

   Blue Monday,
      (a) a Monday following a Sunday of dissipation, or itself
          given to dissipation (as the Monday before Lent).
      (b) a Monday considered as depressing because it is a
          workday in contrast to the relaxation of the weekend.


   Blue ointment (Med.), mercurial ointment.

   Blue Peter (British Marine), a blue flag with a white
      square in the center, used as a signal for sailing, to
      recall boats, etc. It is a corruption of blue repeater,
      one of the British signal flags.

   Blue pill. (Med.)
      (a) A pill of prepared mercury, used as an aperient, etc.
      (b) Blue mass.

   Blue ribbon.
      (a) The ribbon worn by members of the order of the Garter;
          -- hence, a member of that order.
      (b) Anything the attainment of which is an object of great
          ambition; a distinction; a prize. "These
          [scholarships] were the --blue ribbon of the college."
          --Farrar.
      (c) The distinctive badge of certain temperance or total
          abstinence organizations, as of the --Blue ribbon
          Army.

   Blue ruin, utter ruin; also, gin. [Eng. Slang] --Carlyle.

   Blue spar (Min.), azure spar; lazulite. See Lazulite.

   Blue thrush (Zool.), a European and Asiatic thrush
      (Petrocossyphus cyaneas).

   Blue verditer. See Verditer.

   Blue vitriol (Chem.), sulphate of copper, a violet blue
      crystallized salt, used in electric batteries, calico
      printing, etc.

   Blue water, the open ocean.

   Big Blue, the International Business Machines corporation.
      [Wall Street slang.] PJC

   To look blue, to look disheartened or dejected.

   True blue, genuine and thorough; not modified, nor mixed;
      not spurious; specifically, of uncompromising
      Presbyterianism, blue being the color adopted by the
      Covenanters.
      [1913 Webster]

            For his religion . . .
            'T was Presbyterian, true blue.       --Hudibras.
      [1913 Webster]

WordNet (r) 3.0 (2006):

blue vitriol
    n 1: hydrated blue crystalline form of copper sulfate [syn:
         blue vitriol, blue copperas, blue stone,
         chalcanthite]