| Noun | 1. | dark matter - (cosmology) a hypothetical form of matter that is believed to make up 90 percent of the matter in the universe; it is invisible (does not absorb or emit light) and does not collide with atomic particles but exerts gravitational forcematter, substance - that which has mass and occupies space; "an atom is the smallest indivisible unit of matter" weakly interacting massive particle, WIMP - a hypothetical subatomic particle of large mass that interacts weakly with ordinary matter through gravitation; postulated as a constituent of the dark matter of the universe | |