1 a: one that rubs b: an instrument or object (as a rubber eraser) used in rubbing, polishing, scraping, or cleaning c: something that prevents rubbing or chafing 2[from its use in erasers]a: an elastic substance that is obtained by coagulating the milky juice of any of various tropical plants (as of the genera Hevea and Ficus), is essentially a polymer of isoprene, and is prepared as sheets and then dried —called also caoutchouc, india rubberb: any of various synthetic rubberlike substances c: natural or synthetic rubber modified by chemical treatment to increase its useful properties (as toughness and resistance to wear) and used especially in tires, electrical insulation, and waterproof materials 3: something made of or resembling rubber: as a: a rubber overshoe b (1): a rubber tire (2): the set of tires on a vehicle c: a rectangular slab of white rubber in the middle of a baseball infield on which a pitcher stands while pitching d:condom 1