The most common and most likely answer to this crossword clue is the 6 letter word SEPTAL
I've seen this crossword clue in Financial Times
S
E
P
T
A
L
More clues leading to the result SEPTAL
Buddy explains!

The straight part
We know that "mural" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mural = septal.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 SEPTAL mean?
SEPTAL adjective- Of or pertaining to the septum.
- Relating to an Irish clan or sept.