Line used in particular campaign (3)
I believe the answer is:
arc
'line' is the definition.
(I know that arc is a type of curve)
'in particular campaign' is the wordplay.
'in' says the answer is hidden in the clue.
'ARC' can be found hidden inside 'particular campaign'.
'used' is the link.
(Other definitions for arc that I've seen before include "Semi-circle" , "Bow" , "Part of a curve" , "cut off from the circle" , "Electrical spark" .)