The most common and most likely answer to this crossword clue is the 6 letter word CORBEL
C
O
R
B
E
L
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The straight part
We know that "wall bracket" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case wall bracket = corbel.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 CORBEL mean?
CORBEL noun- A structural member jutting out of a wall to carry a superincumbent weight.
- To furnish with a corbel or corbels; to support by a corbel; to make in the form of a corbel.