These may cut lines on graph (4)
I believe the answer is:
axes
'lines on graph' is the definition.
(X axis and Y axis)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for axes that I've seen before include "Drastically cuts" , "Dispenses with" , "Terminates" , "Cutting tools" , "Choppers" .)