Difficult to endure cut close to bone (6)
I believe the answer is:
'difficult' is the definition.
(I've seen this before)
'endure cut close to bone' is the wordplay.
I cannot really understand how this works, but
'cut' could be 'sever' (severing is a kind of cutting) and 'sever' is found in the answer.
A single letter 'e' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
'to' is the link.
Can you help me to learn more?
(Other definitions for severe that I've seen before include "Austere, spartan", "Stern, austere", "Grave", "Harsh and stringent", "Austere, grim".)