Consider wrong woman to undermine and demonstrate (10)
I believe the answer is:
disapprove
'consider wrong' is the definition.
(synonyms)
'woman to undermine and demonstrate' is the wordplay.
'woman' becomes 'Di' (short for Diana).
'to undermine' becomes 'sap' (sapping is a kind of undermining).
'and' means one lot of letters go next to another.
'demonstrate' becomes 'prove' (proving is a kind of demonstrating).
'di'+'sap'+'prove'='DISAPPROVE'
(Other definitions for disapprove that I've seen before include "Censure" , "Not like" , "Not be happy with" , "mind" , "Reject" .)