Tool cauterises wound after third of stitches removed (9)
I believe the answer is:
secateurs
'tool' is the definition.
(gardening tool)
I don't understand the rest of the clue.
(Other definitions for secateurs that I've seen before include "Pruning tool" , "Gardener's tool" , "They make cuts" , "Small pruning shears" , "Clippers used for pruning plants" .)