The most common and most likely answer to this crossword clue is the 12 letter word RETRENCHMENT
I've seen this crossword clue in Financial Times
R
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Buddy explains!
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 RETRENCHMENT mean?
RETRENCHMENT noun- A curtailment or reduction.
- A defensive work constructed within a fortification to make it more defensible by allowing defenders to retreat into and fight from it even after the enemy has taken the outer work.