Wrong about grand gesture (4)
I believe the answer is:
sign
'gesture' is the definition.
(sign is a kind of gesture)
'wrong about grand' is the wordplay.
'wrong' becomes 'sin' (I've seen this before).
'about' is an insertion indicator.
'grand' becomes 'g' ('G' can be a synonym of 'grand').
'sin' placed around 'g' is 'SIGN'.
(Other definitions for sign that I've seen before include "Put one's name to a document" , "add name" , "Evidence" , "Signal, gesture" , "Indicator" .)