A tenacious, elastic, gummy substance obtained from the milky sap of several plants of tropical South America (esp. the euphorbiaceous tree Siphonia elastica or Hevea caoutchouc), Asia, and Africa. Being impermeable to liquids and gases, and not readly affected by exposure to air, acids, and alkalies, it is used, especially when vulcanized, for many purposes in the arts and in manufactures. Also called India rubber (because it was first brought from India, and was formerly used chiefly for erasing pencil marks) and gum elastic. See Vulcanization.