Keen student's wife ensconced in boozer (4)
I believe the answer is:
swot
'keen student's' is the definition.
'wife ensconced in boozer' is the wordplay.
'wife' becomes 'w'.
'ensconced in' is an insertion indicator.
'boozer' becomes 'sot' (I've seen this in other clues).
'w' going within 'sot' is 'SWOT'.
(Other definitions for swot that I've seen before include "Overly studious pupil" , "One studying a lot" , "Intensive studier" , "Study too much - or the student" , "Study assiduously" .)