To overlock is to finish a raw edge so it cannot fray. Overlock the seam, an overlocked edge, overlock the hem.
The machine that does it trims and stitches in one pass, wrapping thread round the edge, which is why factory clothes have those looped seams inside. An overlocker takes several threads at once and is a separate machine from an ordinary sewing one.
1verboverlockTo finish a raw edge so it cannot fray.
“She overlocked the edges of the cotton so the dress would last through years of washing.”
overlock is a finishing.
Over plus lock, from the way the thread locks over the edge of the cloth.
Middle English
lok
English
lock
English, today
overlock
From over + lock. lock comes from Middle English lok. From Middle English lok, from Old English loc, from Proto-West Germanic lok, from Proto-Germanic luką from Proto-Indo-European lewg- (“to bend; turn”). Cognate with cim loch, lòch (“hole”), Dutch lok (“hole”), German Loch (“hole”), German Low German Lock (“hole”), lb Lach (“hole”), wym łöch (“hole”), Yiddish לאָך (“hole”), Danish låg (“lid, cover”), Norwegian Bokmål lokk (“lid, cover”), Norwegian Nynorsk lok, lokk (“lid, cover”).
Etymology from Wiktionary, CC BY-SA