(physics) The amount of fissile material needed to support a self-sustaining nuclear chain reaction. / (figuratively) The tipping point.

(physics) The increased mass of an object moving at relativistic speed relative to an observer.

(chemistry) The mass of an individual molecule of an element or compound.

The starvation of a large proportion of a region's population due to drought, warfare, famine or similar events.

(astronomy) A unit, equal to the mass of the sun, used to express the mass of other stars etc. 1 M_☉ = 2 × 10³⁰ kg.

plural of mass grave

(meteorology) A particular volume of air, especially one having a roughly uniform temperature, pressure and water vapour content.

(military) A body of troops held in military reserve by a general for striking a blow on an exposed flank or wherever the enemy reveals a weak spot.

(Christianity) A religious card that states that a Catholic Mass has been said in honour of a dead person, or as a request for special favours such as improved health or success in a worldly endeavour.

A grave containing many corpses.