Careless, having drunk gin -- gentle! (9)
I believe the answer is:
negligent
'careless' is the definition.
('negligent' can be similar in meaning to 'careless')
'drunk gin gentle' is the wordplay.
'drunk' indicates anagramming the letters.
'gin'+'gentle'='gingentle'
'gingentle' is an anagram of 'NEGLIGENT'.
'having' is the link.
(Other definitions for negligent that I've seen before include "Failing to take due care" , "Of the study of insects" , "Failing to take proper care" , "slack" , "Careless, remiss" .)