Check out in US president a measure of cant (8)
I believe the answer is:
gradient
'a measure of cant' is the definition.
I can't tell whether this defines the answer.
'check out in us president' is the wordplay.
'check out' becomes 'die' ('check out' can informally mean to die).
'in' means one lot of letters goes inside another.
'us president' becomes 'grant' (I've seen this before).
'die' inserted inside 'grant' is 'GRADIENT'.
Can you help me to learn more?
(Other definitions for gradient that I've seen before include "Third OT book" , "Level of steepness" , "Angle of slope" , "Measure of slope" , "Degree of slope in a road" .)