Last to demonstrate this? (9)
I believe the answer is:
'demonstrate this?' is the definition.
The definition suggests a singular noun which matches the answer.
'last' is the wordplay.
I cannot really see how this works, but
'last' could be 'end' (I've seen this in another clue) and 'end' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'to' is the link.
Can you help me to learn more?
(Other definitions for endurance that I've seen before include "Stoicism" , "Ability to withstand hardship for long periods" , "Stoical attitude" , "Ill-fated vessel" , "Stamina" .)