Tells bishops not to start (7)
I believe the answer is:
relates
'tells' is the definition.
(relating is a kind of telling)
'bishops not to start' is the wordplay.
'bishops' becomes 'prelates' (I've seen this before).
'not to start' means to remove the first letter.
'prelates' with its first letter taken away is 'RELATES'.
(Other definitions for relates that I've seen before include "Narrates" , "Describes" , "couples" , "Tells (a tale)" .)