The most common and most likely answer to this crossword clue is the 6 letter word DEBRIS
I've seen this crossword clue in The Guardian
D
E
B
R
I
S
More clues leading to the result DEBRIS
- Rubbish teacher has qualification returned
- Broken fragments presenting girl with no end of danger
- Rubbish in plot upset gentleman turning up
- Partly hide Bristol’s scattered rubbish
- Wreckage found in Harbourside, Bristol
- Ruins girl entering high society with gentleman after rejection
- Society girl knight rejected? Rubbish!
- Brides mistakenly refuse
- Rubble found by young socialites touring Rhode Island
- Conclude Bristol is packed with dross
Buddy explains!

The straight part
We know that "all that remains/all that remains" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case all that remains/all that remains = debris.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 DEBRIS mean?
DEBRIS noun- Rubble, wreckage, scattered remains of something destroyed.
- Litter and discarded refuse.
- The ruins of a broken-down structure.
- Large rock fragments left by a melting glacier etc.