"dark matter." YourDictionary, n.d. Web. 15 October 2018. <http://www.yourdictionary.com/dark-matter>.
dark matter. (n.d.). Retrieved October 15th, 2018, from http://www.yourdictionary.com/dark-matter
Matter that emits little or no detectable radiation of its own, postulated to account for observed gravitational forces that affect astronomical objects but have no observable sources. Dark matter is thought to be part of the missing mass.