Dishonest Khan unexpectedly retaining power (7)
I believe the answer is:
knavish
'dishonest' is the definition.
(I've seen this before)
'khan unexpectedly retaining power' is the wordplay.
'unexpectedly' indicates an anagram.
'retaining' means one lot of letters goes inside another (inserted letters are held or retained).
'power' becomes 'vis' (I've seen this in another clue).
'khan' with letters rearranged gives 'knah'.
'knah' going around 'vis' is 'KNAVISH'.
(Other definitions for knavish that I've seen before include "Villainous" , "Wily" , "like a rogue" , "Dishonest, unscrupulous" , "like one able to beat ten?" .)