A cordial piece of frantic assistance (6)
I believe the answer is:
cassis
'a cordial' is the definition.
(type of cordial drink)
'piece of frantic assistance' is the wordplay.
'piece of' indicates the answer is hidden within the clue.
'CASSIS' can be found hidden inside 'frantic assistance'.
(Other definitions for cassis that I've seen before include "Blackcurrent liqueur" , "French blackcurrant mixer" , "Syrupy blackcurrant liqueur" , "Syrupy blackcurrant drink or flavouring" , "Liqueur made with blackcurrants" .)