The most common and most likely answer to this crossword clue is the 6 letter word PHASER
I've seen this crossword clue in Independent
P
H
A
S
E
R
More clues leading to the result PHASER
Buddy explains!

The straight part
We know that "stunner" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stunner = phaser.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 PHASER mean?
PHASER noun- An electronic device that produces special effects on the sound produced by an electric guitar etc.
- Fictional energy weapon, with multiple settings for degree of intensity, from the television series Star Trek (1966–69).
- To shoot with a phaser weapon.