Quick foray, seizing power (5)
I believe the answer is:
rapid
'quick' is the definition.
('rapid' can be a synonym of 'quick')
'foray seizing power' is the wordplay.
'foray' becomes 'raid' ('raid' can be a synonym of 'foray').
'seizing' indicates putting letters inside.
'power' becomes 'p'.
'raid' enclosing 'p' is 'RAPID'.
(Other definitions for rapid that I've seen before include "Fast, quick" , "Zippy" , "Happening quickly" , "Waterway where the current runs very fast" , "Electrical connector" .)