Expecting to start late exercising power (7)
I believe the answer is:
regnant
'exercising power' is the definition.
Both the answer and definition are adjectives. Perhaps there's an association between them I don't understand?
'expecting to start late' is the wordplay.
'expecting' becomes 'pregnant' (expecting can mean expecting a child).
'to start late' means to remove the first letter (I've seen 'starting late' mean this (the word begins later than normal)).
'pregnant' with its first letter removed is 'REGNANT'.
Can you help me to learn more?
(Other definitions for regnant that I've seen before include "Reigning" , "exercising authority" , "Ruling" , "On the throne" , "Current" .)