Former gesture, completely accurate (5)
I believe the answer is:
exact
'completely accurate' is the definition.
(I've seen this before)
'former gesture' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'gesture' becomes 'act' (I am not sure about this - if you are sure you should believe this answer much more).
'ex'+'act'='EXACT'
Can you help me to learn more?
(Other definitions for exact that I've seen before include "Precise and strictly correct" , "Precisely correct" , "On the nail" , "Strict" , "Absolutely accurate or correct" .)