Vain journalist pursues fanciful notion (9)
I believe the answer is:
conceited
'vain' is the definition.
(synonyms)
'journalist pursues fanciful notion' is the wordplay.
'journalist' becomes 'ed' (short for editor).
'pursues' means one lot of letters go next to another.
'fanciful notion' becomes 'conceit' (I've seen this before).
'ed' after 'conceit' is 'CONCEITED'.
(Other definitions for conceited that I've seen before include "Swollen-headed" , "Vain, having swelled head" , "Vain; narcissistic" , "Stuck-up" , "Very proud of oneself" .)