Fool taken in by canard spun by prophet of doom (9)
I believe the answer is:
cassandra
'prophet of doom' is the definition.
(I've seen this before)
'fool taken in by canard spun' is the wordplay.
'fool' becomes 'ass' (both can mean a stupid person).
'taken in by' means one lot of letters goes inside another.
'spun' indicates anagramming the letters.
'canard' with letters rearranged gives 'candra'.
'ass' going within 'candra' is 'CASSANDRA'.
'by' is the link.
(Other definitions for cassandra that I've seen before include "Greek prophetess who foretold evil events, but was never believed" , "one anticipating disaster" , "Greek who predicted" , "Crass Dana as prophetess of disaster" , "was unbelievable" .)