completely satisfactory
"his smile said that everything was copacetic"
"You had to be a good judge of what a man was like, and the English was copacetic"
Fine, excellent, OK, in excellent order.
The word likely originated from Irving Bacheller's 1919 novel A Man for the Ages, where he invented it as a unique term for a fictional character. Its popularity grew in the 1920s after being featured in the song "At the New Jump Steady Ball."