One on a bender it turned out, drunk (10)
I believe the answer is:
inebriated
'drunk' is the definition.
(inebriating is a kind of drinking)
'one on a bender it turned out' is the wordplay.
'one' becomes 'i' (Roman numeral**).
'on' means one lot of letters go next to another.
'turned out' indicates an anagram.
'a'+'bender'+'it'='abenderit'
'abenderit' anagrammed gives 'nebriated'.
'i'+'nebriated'='INEBRIATED'
(Other definitions for inebriated that I've seen before include "Tipsy" , "wasted" , "Bombed" , "Drunk" .)