Brainbox: swot seen outside Ulster University? (7)
I believe the answer is:
cranium
'brainbox' is the definition.
(I've seen this before)
'swot seen outside ulster university?' is the wordplay.
'swot' becomes 'cram' (synonyms).
'seen outside' means one lot of letters goes inside another.
'ulster' becomes 'NI' (Northern Ireland).
'university?' becomes 'u' (abbreviation for university).
'ni'+'u'='niu'
'cram' enclosing 'niu' is 'CRANIUM'.
(Other definitions for cranium that I've seen before include "hard case" , "The skull, major head bone" , "Brainbox" , "Skull that encloses the brain" , "Part of the skull" .)