The most common and most likely answer to this crossword clue is the 11 letter word HALF-COCKED
I've seen this crossword clue in Independent
H
A
L
F
-
C
O
C
K
E
D
Buddy explains!
The straight part
We know that "not thoroughly prepared" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not thoroughly prepared = half-cocked.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 HALF-COCKED mean?
HALF-COCKED adjective- (of a gun) Not fully cocked
- (of a plan etc) Not fully prepared