E for expert? (7)
I believe the answer is:
egghead
This could be a double definition.
'e for' is the first definition.
The definition suggests a singular noun which matches the answer.
'expert?' is the second definition.
(I've seen this before)
(Other definitions for egghead that I've seen before include "scholar" , "Cracked" , "where soldiers may take a dip?" , "brain" , "providing access to soldiers" .)