Very keen to grasp fabulous wit (8)
I believe the answer is:
ravenous
'very keen to grasp' is the definition.
I can't judge whether this defines the answer.
'fabulous wit' is the wordplay.
'fabulous' becomes 'rave' (I can't explain this - if you can you should believe this answer much more).
'wit' becomes 'nous' (both can mean common sense).
'rave'+'nous'='RAVENOUS'
Can you help me to learn more?
(Other definitions for ravenous that I've seen before include "needing to be fed" , "Voraciously hungry" , "Famished" , "starved?" , "A nervous way to be very hungry" .)