In very difficult — possibly final — circumstances (2,8)
I believe the answer is:
in extremis
'in' is the definition.
Both the answer and definition are adverbs. Perhaps they are linked in a way I don't understand?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for in extremis that I've seen before include "at a desperate point" , "feeling desperation" , "as last resort" , "At the point of death" , "dying" .)