1. A unified body of matter that forms a whole but has no specific shape: a mass of clay. 2. A grouping of individual parts or elements that compose a unified body of unspecified size or quantity. 3. Done or carried out on a large scale. 4. A property of matter equal to the measure of the amount of matter contained in or constituting a physical body that partly determines the body’s resistance to changes in the speed or direction of its motion. The mass of an object is not dependent on gravity and therefore is different from but proportional to its weight. 5. Psychic and emotional energy have mass as per E=MC².