Extremely abstruse answers developed knowledge (9)
I believe the answer is:
awareness
'knowledge' is the definition.
(awareness is a kind of knowledge)
'extremely abstruse answers developed' is the wordplay.
'extremely' suggests removing the centre (only the extremes of the word are used).
'developed' indicates anagramming the letters.
'abstruse' with its centre removed is 'ae'.
'ae'+'answers'='aeanswers'
'aeanswers' with letters rearranged gives 'AWARENESS'.
(Other definitions for awareness that I've seen before include "Knowing" , "State of being conscious" , "Mindfulness, consciousness" , "Consciousness,knowingness" , "Fact of consciousness" .)