Fashionable young thing, Kay Short (4)
I believe the answer is:
chic
'fashionable' is the definition.
(chic means stylish or fashionable)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for chic that I've seen before include "Stylish and elegant - in France" , "style?" , "Modish" , "Stylishly turned out" , "Fashionably elegant" .)