This article is from the alt.usage.english FAQ, by Mark Israel misrael@scripps.edu with numerous contributions by others.
This word, meaning "extremely satisfactory", was first recorded
in 1919, and was originally heard chiefly among U.S. black jazz
musicians. The tap dancer Bill "Bojangles" Robinson (1878-1949)
popularized the word, and claimed to have coined it when he was a
shoeshine boy in Richmond; but a number of Southerners testified
that they had heard the word used by parents or grandparents in the
late 19th century. Suggested origins include: a supposed Italian
word "copacetti"; a Creole French word "coupersetique" meaning "that
can be coped with"; and the Hebrew phrase "kol besedeq" "all with
justice". RHUD2 says that all these theories "lack supporting
evidence".
 
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