It’s possible that this word — meaning that something is in excellent order or satisfactory — has created more column inches of speculation in the USA than any other apart from OK. It’s rare to the point of invisibility outside North America. People mostly become aware of it in the sixties as a result of the US space program — it’s very much a Right Stuff kind of word.
The first stages of the flight of Apollo 10, like most of the flights that led up to it, have gone like clockwork. In the words of ground control at Houston, everything has been “copacetic” — a term of undetermined origin which means perfect.
Chicago Tribune, 20 May 1969.
But even in the USA it doesn’t have the circulation it did thirty years ago. Dictionaries are cautious about attributing a source for it, reasonably so, as there are at least five competing explanations, with no very good evidence for any of them.
One suggestion that’s commonly put forward is that it was originally a word of the African-American community in the USA. The name of Bill “Bojangles” Robinson, a famous black tap-dancer, singer and actor of the period round the turn of the twentieth century is commonly linked to this belief about its origin. Indeed, he claimed to have invented it as a shoeshine boy in Richmond. But other blacks, especially Southerners, said later that they had heard it earlier than Mr Robinson’s day. But he certainly did a lot to popularise the word.
A more frequent explanation is that it derives from one of two Hebrew phrases, hakol b’seder, “all is in order”, or kol b’tzedek, “all with justice”; it is suggested these were introduced into the USA by Yiddish-speaking Jewish immigrants. Yet other accounts say it derives from a Chinook word copasenee, “everything is satisfactory”, once used on the waterways of Washington State, or from the French coupersetique, from couper, “to strike”, or from the French phrase copain(s) c’est épatant! (“buddy(s), that’s great!”), or, in a hugely strained derivation, from the cop is on the settee, supposedly a hoodlum term used to describe a policeman who was not actively watching out for crime, and so one who was OK.
We may agree that most of these suggestions are extremely implausible. Leaving theories aside, the first clear sighting of the word is in a biography of Abraham Lincoln, very popular in its day:
“Now there’s the kind of a man! Stout as a buffalo an’ as to looks I’d call him, as ye might say, real copasetic.” Mrs. Lukins expressed this opinion solemnly and with a slight cough. Its last word stood for nothing more than an indefinite depth of meaning.
A Man for the Ages, by Irving Bacheller, 1919.
Did Mr Bacheller invent the word, as has been suggested? Possibly. We’ve no way of knowing, though I'd guess not. It’s certainly an anachronism.