Prompt student included hint (4)
I believe the answer is:
clue
'hint' is the definition.
(I know that hint can be written as clue)
'prompt student included' is the wordplay.
'prompt' becomes 'cue' (cue can mean a prompt or signal).
'student' becomes 'l' (as in L-plates for learner drivers).
'included' indicates putting letters inside.
'cue' enclosing 'l' is 'CLUE'.
(Other definitions for clue that I've seen before include "What's this" , "One of twenty-four in this puzzle" , "Luce (anag.)" , "Aid to solving" , "Hint, tip" .)