The most common and most likely answer to this crossword clue is the 6 letter word DEFORM
D
E
F
O
R
M
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The straight part
We know that "buckle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case buckle = deform.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 DEFORM mean?
DEFORM verb- To change the form of, usually negatively; to give (something) an unusual or abnormal shape.
- To change the looks of, usually negatively; to give something an unusual or abnormal appearance.
- To mar the character of.
- To alter the shape of by stress.
- To become misshapen or changed in shape.
- Having an unusual and unattractive shape.