the sight nearest the breech of a firearm.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for rear sight
The front sight must be seen through the middle of the rear-sight notch, the top being on a line with the top of the notch.
British Dictionary definitions for rear sight
the sight of a gun nearest to the breech
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