Old saw that's lost its edge? (6)
I believe the answer is:
cliche
'old saw' is the definition.
(I've seen this in another clue)
I don't understand the remainder of the clue.
(Other definitions for cliche that I've seen before include "Banal phrase" , "Phrase made tedious through repetition" , "Truth uttered so often as to become boring" , "One by one" , "Saying made tedious through repetition" .)