Definition of "countersign" [coun•ter•sign]

• To sign (a previously signed document), as for authentication. (verb-transitive)
• A second or confirming signature, as on a previously signed document. Also called countersignature. (noun)
• A sign or signal to be given to a sentry in order to obtain passage; a password. (noun)
• A secret sign or signal given in answer to another. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Upon their approach to the bridge, the challenge, and interchange of sign and countersign, which is usual on such occasions, took place in due form; and as Rudolph’s party filed off one after another into the castle, he commanded them to wake their companions, with whom he intended to renew the patrol, and at the same time to send a relief to Arthur Philipson, whose watch on the bridge was now ended."
• "Ms. KEEPSEAGLE: How they treated us was every time my husband, George, needed to get some money to do repairs, he had to drive, like, 17 miles to the FSA office, get their approval, they would countersign the check."
• "The dancing and singing function primarily as a decoy from the main event happening in this inner sanctum; only we, the viewers, are ushered in to witness the underbelly, to glimpse the politics taking place in the dark, which countersign the frivolities in the flashing sunlight outside."