The most common and most likely answer to this crossword clue is the 11 letter word OSCILLATION
I've seen this crossword clue in The Times
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Buddy explains!
The straight part
We know that "swing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case swing = oscillation.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 OSCILLATION mean?
OSCILLATION noun- The act of oscillating or the state of being oscillated
- A regular periodic fluctuation in value about some mean
- A single such cycle
- (of a function) defined for each point x in the domain of the function by \inf\left\{\mathrm{diam}(f(U))\mid U\mathrm{\ is\ a\ neighborhood\ of\ }x\right\}, and describes the difference (possibly ∞) between the limit superior and limit inferior of the function near that point.