Persuade of the truth of (8)
I believe the answer is:
convince
'persuade of the truth of' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for convince that I've seen before include "Satisfy by evidence" , "Win over to your point of view" , "Make believe" , "Persuade someone of the truth of something" , "Satisfy as to truth" .)