The most common and most likely answer to this crossword clue is the 11 letter word INEXPEDIENT
I've seen this crossword clue in The Times
I
N
E
X
P
E
D
I
E
N
T
Buddy explains!

The straight part
We know that "Unwise" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unwise = inexpedient.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 INEXPEDIENT mean?
INEXPEDIENT adjective- Not expedient; not tending to promote a purpose; not tending to the end desired; unsuitable to time and place