a. [ Compar. Bluer superl. Bluest. ] [ OE. bla, blo, blew, blue, livid, black, fr. Icel.blār livid; akin to Dan. blaa blue, Sw. blå, D. blauw, OHG. blāo, G. blau; but influenced in form by F. bleu, from OHG. blāo. ] 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 pygmæus); also applied to a larger species (Ægoceras leucophæus); 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 ]

v. t. [ imp. & p. p. Blued p. pr. & vb. n. Bluing. ] To make blue; to dye of a blue color; to make blue by heating, as metals, etc. [ 1913 Webster ]

n. 1. One of the seven colors into which the rays of light divide themselves, when refracted through a glass prism; the color of the clear sky, or a color resembling that, whether lighter or darker; a pigment having such color. Sometimes, poetically, the sky; as, to fly off into the blue. [ 1913 Webster ]

2. A pedantic woman; a bluestocking. [ Colloq. ] [ 1913 Webster ]

3. pl. [ Short for blue devils. ] Low spirits; a fit of despondency; melancholy. [ Colloq. ] [ 1913 Webster ]

Berlin blue, Prussian blue. --
Mineral blue. See under Mineral. --
Prussian blue. See under Prussian. [ 1913 Webster ]

n. (Zool.) (a) A trout (Salmo oquassa) inhabiting some of the lakes of Maine. (b) A salmon (Oncorhynchus nerka) of the Columbia River and northward. (c) An American river herring (Clupea æstivalis), closely allied to the alewife. [ 1913 Webster ]

n. The hero of a mediæval French nursery legend, who, leaving home, enjoined his young wife not to open a certain room in his castle. She entered it, and found the murdered bodies of his former wives. -- Also used adjectively of a subject which it is forbidden to investigate. [ 1913 Webster ]

The Bluebeard chamber of his mind, into which no eye but his own must look. Carlyle. [ 1913 Webster ]

n. (Bot.) (a) A plant of the genus Campanula, especially the Campanula rotundifolia, which bears blue bell-shaped flowers; the harebell. (b) A plant of the genus Scilla (Scilla nutans). [ 1913 Webster ]

n. [ Cf. Blaeberry. ] (Bot.) The berry of several species of Vaccinium, an ericaceous genus, differing from the American huckleberries in containing numerous minute seeds instead of ten nutlets. The commonest species are Vaccinium Pennsylvanicum and Vaccinium vacillans. Vaccinium corymbosum is the tall blueberry. [ 1913 Webster ]

n. (Zool.) A duck of the genus Fuligula. Two American species (Fuligula marila and Fuligula affinis) are common. See Scaup duck. [ 1913 Webster ]

n. (Zool.) A small song bird (Sialia sialis), very common in the United States, and, in the north, one of the earliest to arrive in spring. The male is blue, with the breast reddish. It is related to the European robin. [ 1913 Webster ]

Pairy bluebird (Zool.), a brilliant Indian or East Indian bird of the genus Irena, of several species. [ 1913 Webster ]

adj. unable to see the color blue or to distinguish the colors blue and yellow.
Syn. -- tritanopic. [ WordNet 1.5 ]