Pinch secret code after turning up (3)
I believe the answer is:
nip
'pinch' is the definition.
(synonyms)
'secret code after turning up' is the wordplay.
'secret code' becomes 'pin' (personal identification number).
'after turning up' says the letters should be written backwards.
'pin' written backwards gives 'NIP'.
(Other definitions for nip that I've seen before include "little drink" , "severe cold" , "Pinch; quantity of spirits" , "Pinch; bite" , "Pinch, short drink" .)