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dim matter

American  

noun

  1. Astronomy. matter whose low level of luminosity makes it difficult to detect visually but whose gravitational effect on other matter is readily observed.

dim matter Scientific  

  1. Matter that is presumed to exist because of the gravitational effect it has on other matter but that is difficult to observe directly because of its very low luminosity.

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Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.