Endlessly carp? Coming round in the end (5)
I believe the answer is:
finis
'the end' is the definition.
(I've seen this before)
'endlessly carp? coming round in' is the wordplay.
'endlessly' means to remove the last letter.
'carp?' becomes 'fish' (carp is a kind of fish).
'coming round' means one lot of letters goes inside another.
'fish' with its last letter taken off is 'fis'.
'fis' placed around 'in' is 'FINIS'.
(Other definitions for finis that I've seen before include "conclusion!" , "End (of book or film)" .)