Courageous and fortunate in pursuit of power (6)
I believe the answer is:
plucky
'courageous' is the definition.
(similar in meaning)
'fortunate in pursuit of power' is the wordplay.
'fortunate' becomes 'lucky' (associated in meaning).
'in pursuit of' is a charade indicator (letters next to each other) (some letters chase after others).
'power' becomes 'p' (symbol in physics).
'lucky' after 'p' is 'PLUCKY'.
'and' acts as a link.
(Other definitions for plucky that I've seen before include "Brave in English way" , "with bottle" , "Brave, showing courage" , "Doughty" , "Feisty, gutsy" .)