Show lack of interest in short cardigan (5)
I believe the answer is:
shrug
'show lack of interest' is the definition.
(a shrug indicates a lack of interest)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for shrug that I've seen before include "Gesture involving the shoulders" , "Show lack of concern" , "Body language indicating indifference or resignation" , "Shoulder movement to show indifference or resignation" , "indifferent response" .)