Facing work, advance with energy (8)
I believe the answer is:
opposite
'facing' is the definition.
(as in two things facing each other)
'work advance with energy' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'advance' becomes 'posit' (both can mean to put forward or suggest).
'with' is a charade indicator (letters next to each other).
'energy' becomes 'e' (physics symbol as in E=mc2).
'op'+'posit'+'e'='OPPOSITE'
(Other definitions for opposite that I've seen before include "Contrary, antithetical" , "reverse, in fact" , "Rival" , "Facing on the other side" , "Facing - reverse" .)