Inflammation ends in callous: almost unbearably sore (4)
I believe the answer is:
stye
'inflammation' is the definition.
(I've seen this before)
'ends in callous almost unbearably sore' is the wordplay.
'ends in' says to take the final letters.
The final letters of 'callous almost unbearably sore' are 'STYE'.
(Other definitions for stye that I've seen before include "Eyelid infection" , "Tamworth residence" , "Red eye" , "Climb" , "dump" .)