The most common and most likely answer to this crossword clue is the 12 letter word STRAITJACKET
I've seen this crossword clue in The Daily Telegraph
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Buddy explains!
The straight part
We know that "A case for arms limitation" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a case for arms limitation = straitjacket.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 STRAITJACKET mean?
STRAITJACKET noun- A jacket-like garment with very long sleeves which can be secured in place, thus preventing the wearer from moving his or her arms. Often used in psychiatric hospitals to prevent patients from injuring themselves or others.
- Any situation seen as confining or restricting.
- To put someone into a straitjacket.
- (by extension) To restrict the freedom of, either physically or psychologically.