Someone who commits a mass murder.

Method of transport, usually public, that carries people in greater quantities than a typical private method such as car.

The formalities that accompany a mass burial

Burial of multiple bodies in a mass grave

The mass of an atom. / (proscribed) atomic weight; the average mass of atoms of an element.

The pervasive surveillance of an entire population, or a substantial fraction thereof.

A Roman Catholic Mass celebrated in full ceremonial form, in which the celebrant is assisted by a deacon and a subdeacon and accompanied by acolytes, a thurifer, and a choir.

(mathematics, physics) A point, near, or within a body at which the object's mass can be assumed to be concentrated; it coincides with the centroid for a body of uniform density, and with the centre of gravity in a uniform gravitational field.

US standard spelling of centre of mass.

(physics) The energy present in an object because of its mass