Stop a student getting stock (5)
I believe the answer is:
banal
'stock' is the definition.
(I know that stock can be written as banal)
'stop a student getting' is the wordplay.
'stop' becomes 'ban' (I've seen this in another clue).
'student' becomes 'l' (as in L-plates for learner drivers).
'getting' says to put letters next to each other.
'ban'+'a'+'l'='BANAL'
(Other definitions for banal that I've seen before include "lacking interest?" , "Boring or trivial" , "Tediously unoriginal" , "'Trite, time-worn (5)'" , "Trite and insipid" .)