Copperhead (1861)

[bapopik at AOL.COM]

http://www.barrypopik.com/article/970/copperhead-civil-war-nickname
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It appears that the OED is a year off on this one. "Copperhead" began with a mail incident (snakes, not anthrax) in April 1861. Clearly, the term was in wide circulation by May 1861. I wouldn't look to see who "coined" the term; rather, it seems to flow directly from the April 1861 incident at the Post Office.