Sentence ender (6)
I believe the answer is:
period
'sentence ender' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for period that I've seen before include "End of story" , "Span of time" , "Amount of time - US full stop" , "A portion of time" , "Length of time, or a full stop" .)