Entreaty certain to provide enjoyment (8)
I believe the answer is:
pleasure
'enjoyment' is the definition.
(I've seen this before)
'entreaty certain' is the wordplay.
'entreaty' becomes 'plea' (plea is a kind of entreaty).
'certain' becomes 'sure' (synonyms).
'plea'+'sure'='PLEASURE'
'to provide' is the link.
(Other definitions for pleasure that I've seen before include "A repulse (anag.)" , "Feeling of enjoyment or satisfaction" , "'Enjoyment, delight (8)'" , "Delight, joy" , "entertainment" .)