Former adversary deprived of work, a symbol of power (8)
I believe the answer is:
exponent
'a symbol of power' is the definition.
(symbol showing a power in mathematics)
'former adversary deprived of work' is the wordplay.
'former' becomes 'ex'.
'adversary' becomes 'opponent' (synonyms).
'deprived of' indicates named letters should be taken away.
'work' becomes 'op' (abbreviation for opus).
'opponent' with 'op' removed is 'ponent'.
'ex'+'ponent'='EXPONENT'
(Other definitions for exponent that I've seen before include "index" , "Propagandist" , "Interpretive artist - open next (anag)" , "Interpreter, advocate; (maths.) power" , "Promoter (of an idea or theory)" .)