Endlessly carp? Coming round in the end (5)
I believe the answer is:
Here is my best explanation:
'the end' is the definition.
(I've seen this before)
'endlessly carp? coming round in' is the subsidiary indication.
'endlessly' means to remove the last letter.
'carp?' becomes 'fish' (carp is a kind of fish).
'coming round' is an insertion indicator.
'fish' with its final letter removed is 'fis'.
'fis' going around 'in' is 'finis'.
(Other definitions for finis that I've seen before include "The end", "End (of book or film)" and "conclusion!".)