Being on the slant, it isn't exactly level (5)
I believe the answer is:
bevel
'being on the slant' is the definition.
'bevel' can be an answer for 'slant' (I have seen 'Slant of surface ' mean 'bevel' so perhaps 'slant' could also mean 'bevel'). I am not sure about the 'being on the' bit.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for bevel that I've seen before include "Sloping edge or chamfer" , "Cut at a slant" , "Cut a sloping surface on" , "Tool for making a sloping edge on a piece of wood" , "Sloped edge" .)