He left here with a girl - irresponsible (6)
I believe the answer is:
remiss
'irresponsible' is the definition.
Both the answer and definition are adjectives. Maybe you can see a link between them that I can't see?
'he left here with a girl' is the wordplay.
'left' suggests deleting specific letters.
'with' is a charade indicator (letters next to each other).
'a girl' becomes 'miss' (term of address for an unmarried woman).
'here' with 'he' taken away is 're'.
're'+'miss'='REMISS'
Can you help me to learn more?
(Other definitions for remiss that I've seen before include "Neglectful" , "Failing in what duty requires" , "Negligent, lax" , "Careless and inattentive" , "Derelict in duty" .)