Angled face hides endless suffering (8)
I believe the answer is:
diagonal
'angled' is the definition.
(at a diagonal angle)
'face hides endless suffering' is the wordplay.
'face' becomes 'dial' (face of a clock).
'hides' indicates putting letters inside.
'endless suffering' becomes 'agon' (I can't justify this - if you can you should believe this answer much more).
'dial' going around 'agon' is 'DIAGONAL'.
Can you help me to learn more?
(Other definitions for diagonal that I've seen before include "On a slope" , "Slanting line joining two opposite corners" , "bishop moves here" , "bishop controls it" , "Slanting, from corner to corner" .)