- 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.