I pride myself on my vocabulary, but I'd never heard "copacetic" before - thank you for introducing me to a new word! (In my defence, I see that it's probably an American word rather than an English one.)
Jeremy, Here's the definition from Webster's Unabridged. No one seems to know where it came from:
fine; completely satisfactory; OK.
Also, copasetic, copesetic.
[1915–20, Amer.; of obscure orig; popular attributions of the word to LaF, It, Heb, etc., lack supporting evidence]
When I was growing up in a northern suburb of Detroit my Polish friends used to use it a lot. I always thought it originated in Polish, but I guess not.