Dictionary.com
definitions

relative density

noun Physics.
  1. specific gravity.

Origin of relative density

First recorded in 1875–80
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for relative density

relative density

noun
  1. the ratio of the density of a substance to the density of a standard substance under specified conditions. For liquids and solids the standard is usually water at 4°C or some other specified temperature. For gases the standard is often air or hydrogen at the same temperature and pressure as the substanceSymbol: d See also specific gravity, vapour density
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
relative density in Science

relative density

  1. The ratio of the density of one substance to that of a reference substance, typically water. See more at specific gravity.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.