Believe student, ignoring untruth and cant (5)
I believe the answer is:
bevel
'cant' is the definition.
(I know that cant can be written as bevel)
'believe student ignoring untruth' is the wordplay.
'student' becomes 'L' (as in L-plates for learner drivers).
'ignoring' suggests deleting specific letters.
'untruth' becomes 'lie' (lie is a kind of untruth).
'believe'+'l'='believel'
'believel' with 'lie' taken away is 'BEVEL'.
'and' is the link.
(Other definitions for bevel that I've seen before include "Sloping edge or chamfer" , "Two surfaces that meet at an angle different from 90 degrees" , "Two flat surfaces meeting at other than a right angle" , "Sloping join" , "Cut at a slant" .)