The most common and most likely answer to this crossword clue is the 6 letter word BUCKLE
I've seen this crossword clue in The Times
B
U
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K
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E
More clues leading to the result BUCKLE
- Deer and young bear perhaps raised in cave
- Warp belt’s fastening
- Resist the French or give in?
- It sounds like dollar will collapse
- & 26 UK blunder, breaking with EC? Result: collapse
- Belt up or bend over
- Clasp deer and baby, lying back
- Male will, as they say, give way
- Bend almost all of small shield
- Legislature loses heart following dollar’s collapse
Buddy explains!

The straight part
We know that "Warp/belt’s fastening" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case warp/belt’s fastening = buckle.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 BUCKLE mean?
BUCKLE verb- To distort or collapse under physical pressure; especially, of a slender structure in compression.
- To make bend; to cause to become distorted.
- To give in; to react suddenly or adversely to stress or pressure (of a person).
- To yield; to give way; to cease opposing.
- To enter upon some labour or contest; to join in close fight; to contend.
- To buckle down; to apply oneself.
- A clasp used for fastening two things together, such as the ends of a belt, or for retaining the end of a strap.
- The brisure of an eighth daughter.
- (roofing) An upward, elongated displacement of a roof membrane frequently occurring over insulation or deck joints. A buckle may be an indication of movement with the roof assembly.
- A distortion, bulge, bend, or kink, as in a saw blade or a plate of sheet metal.
- A curl of hair, especially a kind of crisp curl formerly worn; also, the state of being curled.
- A contorted expression, as of the face.
- To fasten using a buckle.
- To unite in marriage.