The most common and most likely answer to this crossword clue is the 5 letter word SWISH
I've seen this crossword clue in The Daily Telegraph
S
W
I
S
H
More clues leading to the result SWISH
Buddy explains!

The straight part
We know that "fashionable" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fashionable = swish.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 SWISH mean?
SWISH noun- A short rustling, hissing or whistling sound, often made by friction.
- A hissing, sweeping movement through the air, as of an animal's tail.
- A sound of liquid flowing inside a container.
- A twig or bundle of twigs, used for administering beatings; a switch
- A successful basketball shot that does not touch the rim or backboard.
- An effeminate male homosexual.
- An improvised alcoholic drink made by fermenting whatever ingredients are available.
- To make a rustling sound while moving.
- To flourish with a swishing sound.
- To flog; to lash.
- To make a successful basketball shot that does not touch the rim or backboard.
- To mince or otherwise to behave in an effeminate manner.
- (transitive) To cause a liquid to move around in a container, or in one's mouth.
- Sophisticated; fashionable; smooth.
- Attractive, stylish
- Effeminate.
- A hissing or whistling sound of something travelling quickly through the air.