Outer limit (3)
'outer limit' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for end that I've seen before include "Termination" , "'Conclusion, finale (3)'" , "Finish, close" , "Cessation, conclusion" , "Time to break-up (3,2,4) - See 12" .)
(Other definitions for extreme that I've seen before include "Exceptional - radical" , "Drastic; outermost" , "Sharp" , "lacking moderation" , "too much" .)