Stitched line (4)
I believe the answer is:
seam
'stitched line' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for seam that I've seen before include "Join - thin layer" , "Fabric joint" , "Sewing join" , "Stratum (of a mineral)" , "Unfasten" .)