Entreaty certain to provide gratification (8)
I believe the answer is:
pleasure
'gratification' 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' ('sure' can be a synonym of 'certain').
'plea'+'sure'='PLEASURE'
'to provide' acts as a link.
(Other definitions for pleasure that I've seen before include "A desirable emotion" , "amusement" , "Feeling of enjoyment or satisfaction" , "Delight, happiness" , "A very desirable feeling" .)