Observed cutting tool (3)
I believe the answer is:
saw
I believe this clue is a double definition.
'observed' is the first definition.
(seen)
'cutting tool' is the second definition.
(I've seen this in another clue)
(Other definitions for saw that I've seen before include "Observed; tool" , "Old saying for woodcutter" , "Viewed; maxim" , "Carpentry tool" , "Carpenter's tool" .)