Courage yielding power and fortune (4)
I believe the answer is:
luck
'fortune' is the definition.
(synonyms)
'courage yielding power' is the wordplay.
'courage' becomes 'pluck' (pluck is a kind of courage).
'yielding' suggests deleting specific letters.
'power' becomes 'p' (symbol in physics).
'pluck' with 'p' removed is 'LUCK'.
'and' is the link.
(Other definitions for luck that I've seen before include "See 1" , "'Fortune, fate (4)'" , "''The devil''s children has the devil's ....'" , "Chance, fate, fortune" , "Good or bad fortune" .)