An Irish secret society organised in 1843. Stout, active young Irishmen, dressed up in women's clothes, blackened faces, and otherwise disguised, to surprise those employed to enforce the payment of rents. Their victims were ducked in bog-holes, and many were beaten most unmercifully.
“The judge who tried the murderer was elected by the Molly Maguires; the jurors who assisted him were themselves Molly Maguires. A score of Molly Maguires came forward to swear that the assassin was sixty miles from the spot on which he had been seen to fire at William Dunn, . . . and the jurors returned a verdict of Not Guilty.” —W. Hepworth Dixon: New America, ii. 28.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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