E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Copperheads.
Secret foes. Copperheads are poisonous serpents of America that give no warning, like rattlesnakes, of their attack. In the great Civil War of the United States the term was applied by the Federals to the peace party, supposed to be the covert friends of the Confederates.
