Dud doctor fled radical - how pretentious! (9)
I believe the answer is:
bombastic
'pretentious' is the definition.
(I've seen this before)
'dud doctor fled radical' is the wordplay.
I cannot quite see how this works, but
'dud' could be 'bomb' (synonyms) and 'bomb' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'how' acts as a link.
Can you help me to learn more?
(Other definitions for bombastic that I've seen before include "Pretentious" , "affected" , "Extravagant" , "High-flown" , "Declamatory, ostentatiously lofty" .)