Having gin, now get drunk (6)
I believe the answer is:
owning
'having' is the definition.
('own' can be a synonym of 'have')
'gin now get drunk' is the wordplay.
'get drunk' indicates an anagram.
'gin'+'now'='ginnow'
'ginnow' anagrammed gives 'OWNING'.
(Other definitions for owning that I've seen before include "Possesing" , "Being in possession or confessing" , "Possessing" , "In legal possession of" , "Admitting" .)