To shout loudly in pain, fear, or anger. The second term appears to have originated as a play on the French expletive morbleu (mort bleu translates as “blue murder”). The Hotten Dictionary of Slang (1859) defined it as a desperate or alarming cry. The term was used by Dion Boucicault about 1874: “They were standing by and trying to screech blue murder” (quoted in M. R. Booth, English Plays of the Nineteenth Century; cited by OED). It is heard less often, at least in America, than the more graphic bloody murder, dating from the first half of the 1900s. For example, “The one-year-old who has yelled bloody murder during his physical . . .” (B. Spock, Problems of Parents, 1962).