Former partner working in confined surroundings is a skilled performer (8)
I believe the answer is:
exponent
'a skilled performer' is the definition.
(I've seen this before)
'former partner working in confined surroundings' is the wordplay.
'former partner' becomes 'ex'.
'working in' becomes 'on' (I've seen this in other clues).
'confined' becomes 'pent' ('pent' can be similar in meaning to 'confined').
'surroundings' means one lot of letters goes inside another.
'on' inserted inside 'pent' is 'ponent'.
'ex'+'ponent'='EXPONENT'
'is' is the link.
(Other definitions for exponent that I've seen before include "Symbol of power" , "index" , "Skilled performer" , "Interpretive artist - open next (anag)" , "Promoter (of an idea or theory)" .)