… bonus almost certain before it's over (7)
I believe the answer is:
surplus
'over' is the definition.
(thesaurus)
'bonus almost certain before' is the wordplay.
'bonus' becomes 'plus' (I've seen this before).
'almost' means to remove the last letter (most of the word but not all of it).
'certain' becomes 'sure' (synonyms).
'before' says to put letters next to each other.
'sure' with its last letter taken off is 'sur'.
'plus' after 'sur' is 'SURPLUS'.
'it's' acts as a link.
(Other definitions for surplus that I've seen before include "Excess, overstock" , "unnecessary" , "Remainder" , "Unneeded extra" , "balance" .)