Prefix with cortex (3)
I believe the answer is:
neo
'prefix with cortex' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for neo that I've seen before include "Prefix meaning new - try one" , "Prefix meaning new of modern form of" , "New (suffix)" , "Hero of The Matrix films; new (prefix)" , "language" .)