Learner in academic stream still (4)
I believe the answer is:
calm
'still' is the definition.
('calm' can be a synonym of 'still')
'learner in academic stream' is the wordplay.
'learner' becomes 'l'.
'in' means one lot of letters goes inside another.
'academic stream' becomes 'cam' (River cam runs through Cambridge).
'l' put within 'cam' is 'CALM'.
(Other definitions for calm that I've seen before include "Peaceful, undisturbed" , "Halcyon" , "Still - force 0 on the Beaufort scale" , "Peaceful and unexcited" , "Imperturbable, soothe" .)