Meaning

noun an elastic material obtained from the latex sap of trees (especially trees of the genera Hevea and Ficus) that can be vulcanized and finished into a variety of products

noun any of various synthetic elastic materials whose properties resemble natural rubber

noun an eraser made of rubber (or of a synthetic material with properties similar to rubber); commonly mounted at one end of a pencil

originFrom rub + -er. The sense of the substance comes from its ability to function as an eraser, displacing earlier caoutchouc. The senses not pertaining to rubbing or erasing are secondarily derived from the name of the substance.

Etymology from Wiktionary, CC BY-SA 3.0