A button hole is the slit a round fastener is pushed through. Sew a button hole.
It is stitched round the edge so the cloth cannot fray or tear open. A button hole in a lapel was originally for a real flower and still holds one at weddings.
button hole is a hole.
Built from
buttonhole Originally buttonhold (“a loop of string to hold a button down”), but changed by folk etymology by influence of hole. by surface analysis, button + hole.
Etymology from Wiktionary, CC BY-SA