Successor to Moses (6)
I believe the answer is:
joshua
'successor to moses' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for joshua that I've seen before include "Israelite leader in Old Testament who fought the battle of Jericho" , "Sixth book of the Old Testament" , "Moses' successor as leader of the Israelites" , "Conqueror of Jericho" , "Sir -- Reynolds, British painter" .)