The most common and most likely answer to this crossword clue is the 8 letter word MUSICALS
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More clues leading to the result MUSICALS
Buddy explains!

The straight part
We know that "Chicago and Oklahoma!" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case chicago and oklahoma! = musicals.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MUSICALS mean?
MUSICALS noun- A stage performance, show or film that involves singing, dancing and musical numbers performed by the cast as well as acting.
- A meeting or a party for a musical entertainment; a musicale.