Well, not exactly sober! (5)
I believe the answer is:
oiled
'sober' is the definition.
Both the definition and answer are adjectives. Perhaps they are linked in a way I don't understand?
'well not exactly' is the wordplay.
'well' becomes 'oil well' (oil well is a kind of well).
'not exactly' becomes 'ed' (I can't explain this - if you can you should believe this answer much more).
'oil'+'ed'='OILED'
Can you help me to learn more?
(Other definitions for oiled that I've seen before include "Greased; drunk" , "Lubricated or drunk" , "Besotted" , "protected from rust?" , "tipsy" .)