Choose as a successor (6)
I believe the answer is:
anoint
'choose as a successor' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for anoint that I've seen before include "Smear (with oil)" , "Bless with holy oil" , "Put in position of authority" , "Bless with sacred oils" , "Consecrate with holy oil" .)