Almost certain to provide yield (9)
I believe the answer is:
surrender
'yield' is the definition.
(yield can mean to give up or surrender)
'almost certain to provide' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'certain' becomes 'sure' (synonyms).
'to' means one lot of letters go next to another.
'provide' becomes 'render' (synonyms).
'sure' with its final letter removed is 'sur'.
'sur'+'render'='SURRENDER'
(Other definitions for surrender that I've seen before include "Hand over" , "Cease resistance" , "Submit (to an opponent)" , "Cede" , "Yield - release" .)