x or y, on graphs (4)
I believe the answer is:
axis
'x or y on graphs' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for axis that I've seen before include "vertebra" , "Central point of a rotation" , "Centre about which something turns" , "Line about which to rotate" , "Alliance of powers eg Germany, Italy and Japan in WWII" .)