Swift attack blocked by prince (5)
I believe the answer is:
rapid
'swift' is the definition.
(I've seen this in another clue)
'attack blocked by prince' is the wordplay.
'attack' becomes 'raid' (raid is a kind of attack).
'blocked by' indicates putting letters inside (block can mean to plug a gap in something).
'prince' becomes 'p' (abbreviation).
'raid' placed around 'p' is 'RAPID'.
(Other definitions for rapid that I've seen before include "Quick or swift" , "Fast, speedy" , "Happening quickly" , "Brisk" , "haste" .)