Success, accepting new suggestion (4)
I believe the answer is:
hint
'suggestion' is the definition.
(I know that hint is a type of suggestion)
'success accepting new' is the wordplay.
'success' becomes 'hit' (a hit is a commercial success).
'accepting' means one lot of letters goes inside another (inserted letters are accepted).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'hit' enclosing 'n' is 'HINT'.
(Other definitions for hint that I've seen before include "Intimate" , "Indirect clue" , "'Slight indication, indirect suggestion (4)'" , "Imply, suggest" , "A dash" .)