A pair of decoys in a rush curse (7)
I believe the answer is:
scourge
'curse' is the definition.
(I know that curse can be written as scourge)
'a pair of decoys in a rush' is the wordplay.
'a pair of decoys' becomes 'co' (I am not sure about this - if you are sure you should believe this answer much more).
'in' indicates putting letters inside.
'a rush' becomes 'surge' ('surge' can be a synonym of 'rush').
'co' inserted inside 'surge' is 'SCOURGE'.
Can you help me to learn more?
(Other definitions for scourge that I've seen before include "One causing great suffering; whip" , "Cause great suffering to (someone); whip" , "One providing lashings" , "Source of great trouble" , "Bane, curse" .)