sempatch

/ˈsɛmpætʃ/
noun
  1. A small piece of fabric used for testing or mending, especially in sewing or tailoring.
    • She cut a sempatch from the scrap bin to test the embroidery stitch.
    • He kept a collection of sempatches in his sewing kit for quick repairs.
    • The tailor used a sempatch to match the color before repairing the coat.
Synonyms