Entreaty certain to give satisfaction (8)
I believe the answer is:
pleasure
'satisfaction' 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 give' is the link.
(Other definitions for pleasure that I've seen before include "amusement" , "Urgent entreaty begins gratification" , "Happy satisfaction" , "entertainment" , "A desirable emotion" .)