Brainbox (5)
'brainbox' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for egghead that I've seen before include "where soldiers may take a dip?" , "Brainiac" , "providing access to soldiers" , "scholar" , "Ovoid-shaped intellectual" .)
'brainbox' is the definition.
(the brain is contained by the skull)
This is the entire clue.
(Other definitions for skull that I've seen before include "Brainbox" , "Head structure" , "The head-bone" , "Bony frame of head ..." , "Brain casing" .)