Satisfaction certain to follow an entreaty (8)
I believe the answer is:
pleasure
'satisfaction' is the definition.
(I know that satisfaction can be written as pleasure)
'certain to follow an entreaty' is the wordplay.
'certain' becomes 'sure' (synonyms).
'to follow' means one lot of letters go next to another.
'an entreaty' becomes 'plea' (plea is a kind of entreaty).
'sure' put after 'plea' is 'PLEASURE'.
(Other definitions for pleasure that I've seen before include "Enjoyment, happiness" , "amusement" , "Delight, happiness" , "Delectation, delight" , "A repulse (anag.)" .)