Finish line marker (4)
I believe the answer is:
tape
'finish line marker' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tape that I've seen before include "Record; material strip" , "Breast this first to win foot-race" , "that race winner may break" , "Fabric strip; record" , "Music cassette" .)