What is the meaning of witchgrass?

noun

• North American grass with slender brushy panicles; often a weed on cultivated land.
  • synonyms: witch grass, old witchgrass, old witch grass, tumble grass, Panicum capillare
• European grass spreading rapidly by creeping rhizomes; naturalized in North America as a weed.
  • synonyms: dog grass, couch grass, quackgrass, quack grass, quick grass, witch grass, Agropyron repens