1. A yellowish, amorphous, elastic material, composed almost entirely of an isoprene polymer, obtained from the milky sap or latex of various tropical plants, especially the rubber tree, and vulcanized, pigmented, finished, and modified into products such as electric insulation, elastic bands and belts, tires, and containers. Also called caoutchouc, India rubber.

2. Any of numerous synthetic elastic materials of varying chemical composition with properties similar to those of natural rubber; an elastomer.

3. A low overshoe made of rubber.

4. Baseball The rectangular piece of hard rubber that the pitcher must remain in contact with when making a pitch.

5. Something made of rubber, as:

6. Slang A condom.

7. One that rubs, especially one that gives a massage.