The most common and most likely answer to this crossword clue is the 8 letter word FRIGHTEN
I've seen this crossword clue in The Daily Telegraph
F
R
I
G
H
T
E
N
More clues leading to the result FRIGHTEN
- Cow just getting stuck in swampy ground
- Scare, being loud? Correct
- Restore to a normal position following earlier alarm
- Screw badly, then drive out
- Shock for Tory in Slough
- Cow not left in lowland
- Spook just seen in bog
- Front part of fridge appropriate space to chill
- Rattle all the way through Slough
- Panic is appropriate being trapped in bog
Buddy explains!

The straight part
We know that "Panic" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case panic = frighten.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 FRIGHTEN mean?
FRIGHTEN verb- To cause to feel fear; to scare; to cause to feel alarm or fright.