The most common and most likely answer to this crossword clue is the 7 letter word TRICKSY
I've seen this crossword clue in The Times
T
R
I
C
K
S
Y
Buddy explains!

The straight part
We know that "Cunning" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cunning = tricksy.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 TRICKSY mean?
TRICKSY adjective- Inclined to trickery; sneaky, devious.