No longer worth debating (4)
I believe the answer is:
moot
'no longer worth debating' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for moot that I've seen before include "Anglo-Saxon assembly; subject to debate" , "Controversial" , "Open to question" , "Such a point is disputable" , "Undecided as a debatable point may be" .)