(formerly) a person who rode post; a mounted mail carrier.
Origin of postrider
First recorded in 1695–1705; post3
Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for postrider
Historical Examples of postrider
Yes, yes, it's Rodney—Rodney and the postrider—they're coming!
Write him a letter—send it by the postrider—urge upon him the enormous importance of his getting here by tomorrow morning.
Now the postrider was to the people of Revolutionary days what the telegraph or the telephone is to us today.
British Dictionary definitions for postrider
(formerly) a person who delivered post on horseback
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