Different actor initially in role within grasp (8)
I believe the answer is:
separate
'different' is the definition.
(thesaurus)
'actor initially in role within grasp' is the wordplay.
'actor initially' becomes 'a' (I can't justify this - if you can you should believe this answer much more).
'in' means one lot of letters goes inside another.
'role' becomes 'part' ('part' can be a synonym of 'role').
'within' indicates putting letters inside.
'grasp' becomes 'see' (both can mean understand or comprehend).
'a' put within 'part' is 'parat'.
'parat' inserted inside 'see' is 'SEPARATE'.
(Other definitions for separate that I've seen before include "Come apart" , "Distinct, not joined" , "Distinct; divide" , "Unconnected" , "Distinct or discrete" .)