Hope a lord will seize power (6)
I believe the answer is:
aspire
'hope' is the definition.
(I've seen this before)
'a lord will seize power' is the wordplay.
'lord' becomes 'sire' (sire is a kind of lord).
'will seize' indicates putting letters inside.
'power' becomes 'p' (symbol in physics).
'sire' enclosing 'p' is 'spire'.
'a'+'spire'='ASPIRE'
(Other definitions for aspire that I've seen before include "Aim at, work towards" , "Persia (anag.)" , "I spare (anag.)" , "Set your sights on" , "Hope, dream" .)