Prompt to include large tip (4)
I believe the answer is:
clue
'tip' is the definition.
(I've seen this in other clues)
'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 "crossword guide" , "Hint towards solution" , "Part of a crossword" , "one of 28 here" , "It helps solve a crime" .)