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.