Here's a page that explores various possible alternative theories as to where copacetic comes from. Some associate it with the orighinal Bo Jangles, a Harlem soft-shoe dancer. Interesting that none of the leads on this page go back to the Chinook jargon reference Roger found, which actually sounds more plausible. There's also a quote of Lord Buckley using the word, which is perhaps where I picked it up.
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