What ruler is expecting to lose power? (7)
I believe the answer is:
regnant
'what ruler is' is the definition.
(I know that ruler are usually regnant)
'expecting to lose power?' is the wordplay.
'expecting' becomes 'pregnant' (expecting can mean expecting a child).
'to lose' indicates named letters should be taken away.
'power?' becomes 'p' (symbol in physics).
'pregnant' with 'p' taken out is 'REGNANT'.
(Other definitions for regnant that I've seen before include "Ruling" , "On the throne" , "Reigning" , "Not like a consort" , "exercising authority" .)