nightrider definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
any of a band of masked, mounted men who perform lawless acts of violence and terror at night to intimidate, terrorize, etc.; esp., any of such a band of white men in the S U.S. after the Civil War
nightrider definition by American Heritage Dictionary
One of a secret band of mounted, usually masked white men who engaged in nocturnal terrorism for revenge or intimidation in the southern United States especially during Reconstruction.