Greeting intellectual first - that's an idea (9)
I believe the answer is:
brainwave
'that's an idea' is the definition.
(I've seen this before)
'greeting intellectual first' is the wordplay.
I cannot really understand how this works, but
'greeting' could be 'wave' (I've seen this before) and 'wave' is located in the answer.
'intellectual' could be 'brain' (brain is a kind of intellectual) and 'brain' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for brainwave that I've seen before include "Sudden bright idea" , "Good idea" , "Great idea" .)