Gesture of indifference (5)
I believe the answer is:
shrug
'gesture of indifference' is the definition.
(a shrug indicates a lack of interest)
This is all the clue.
(Other definitions for shrug that I've seen before include "Indifferent gesture" , "Raise (shoulders) slightly" , "display nonchalance" , "Gesture involving the shoulders" , "Shoulder movement to show indifference or resignation" .)