Ahead, drunk's nervous (7)
I believe the answer is:
uptight
'nervous' is the definition.
(synonyms)
'ahead drunk's' is the wordplay.
'ahead' becomes 'up' (similar in meaning).
'drunk' becomes 'tight' (slang term).
'up'+'tight'='UPTIGHT'
(Other definitions for uptight that I've seen before include "Neurotic" , "Like a tense person" , "Tense - cross" , "Tense, nervous, repressed" , "Tip thug, being nervously tense" .)