Identifying a chap returning with gin cocktail (6)
I believe the answer is:
naming
'identifying' is the definition.
('name' can be a synonym of 'identify')
'a chap returning with gin cocktail' is the wordplay.
'a chap' becomes 'man' (chap can mean a man).
'returning' says the letters should be written backwards.
'with' says to put letters next to each other.
'cocktail' indicates anagramming the letters.
'man' back-to-front is 'nam'.
'gin' anagrammed gives 'ing'.
'nam'+'ing'='NAMING'
(Other definitions for naming that I've seen before include "Identifying, citing" , "Identifying; mentioning" , "Allotting term to" , "Calling" , "Christening" .)