Definitions
1.NounAn extremely bright and massive hypothetical astrophysical object whose illumination is powered by annihilation of dark-matter particles and anti-particles (or by self-annihilation if they are Majorana particles).
2.NounA black hole: star so massive that its escape velocity is above the speed of light, making the star dark, as no light can escape.
3.NounUsed other than figuratively or idiomatically: see dark, star.