Gnat swerves back before net is cast on different course (7)
I believe the answer is:
tangent
But I can't explain it at all! Could you help me understand?
(Other definitions for tangent that I've seen before include "Straight line that touches but does not intersect a curve" , "line in mathematics" , "Line grazing another" , "Particular line" , "mostly irrelevant item" .)