Knife cut drawn up over ambassador's brain (7)
I believe the answer is:
egghead
This clue might be a double definition.
'knife cut drawn up over ambassador's' is the first definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'brain' is the second definition.
(I've seen this before)
Can you help me to learn more?
(Other definitions for egghead that I've seen before include "Boffin" , "providing access to soldiers" , "Intellectual - highbrow" , "An intellectual (inf.)" , "Intellectual (sl.)" .)