Prompt to include large hint (4)
I believe the answer is:
clue
'hint' is the definition.
('clue' can be a synonym of 'hint')
'prompt to include large' is the wordplay.
'prompt' becomes 'cue' ('cue' can be a synonym of 'prompt').
'to include' indicates putting letters inside.
'large' becomes 'l'.
'cue' going around 'l' is 'CLUE'.
(Other definitions for clue that I've seen before include "Aid to solving" , "Hint; piece of evidence" , "Crossword aid" , "Pointer" , "one of 28 here" .)