Nurse about to abandon opposing figure (6)
I believe the answer is:
sister
'nurse' is the definition.
(I've seen this before)
'about to abandon opposing figure' is the wordplay.
'about' becomes 're' (common abbreviation for 'with reference to').
'to abandon' indicates named letters should be taken away.
'opposing figure' becomes 'resister' (someone who resists).
'resister' with 're' taken away is 'SISTER'.
(Other definitions for sister that I've seen before include "woman in hospital" , "trade union member?" , "A relative to resist" , "Resist about the sibling" , "Nun's title" .)