The most common and most likely answer to this crossword clue is the 12 letter word APPREHENSION
I've seen this crossword clue in Financial Times
A
P
P
R
E
H
E
N
S
I
O
N
Buddy explains!
The straight part
We know that "Fear/arrest" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fear/arrest = apprehension.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 APPREHENSION mean?
APPREHENSION noun- The physical act of seizing or taking hold of (something); seizing.
- The act of seizing or taking by legal process; arrest.
- Perception; the act of understanding using one's intellect without affirming, denying, or passing any judgment
- Opinion; conception; sentiment; idea.
- The faculty by which ideas are conceived or by which perceptions are grasped; understanding.
- Anticipation, mostly of things unfavorable; dread or fear at the prospect of some future ill.