Live down under (5)
I believe the answer is:
below
'under' is the definition.
('below' can be a synonym of 'under')
'live down' is the wordplay.
'live' becomes 'be' ('be' can be a synonym of 'live').
'down' becomes 'low' ('low' can be a synonym of 'down'**).
'be'+'low'='BELOW'
(Other definitions for below that I've seen before include "Inferior" , "Lower than" , "Later in text" , "as mentioned later" , "Feel miserable" .)