Very old woman said to predict failure in honest spy (9)
I believe the answer is:
pythoness
'very old woman said to predict' is the definition.
(historical term for an elderly female prophetess)
'failure in honest spy' is the wordplay.
'failure in' indicates an anagram (a broken or failed ordering of the letters).
'honest'+'spy'='honestspy'
'honestspy' with letters rearranged gives 'PYTHONESS'.
(Other definitions for pythoness that I've seen before include "dangerous woman" , "Voice of oracle" .)