Definition of "secret service" [se•cret serv•ice]

• Intelligence-gathering activities conducted secretly by a government agency. (noun)
• A government agency engaged in intelligence-gathering activities. (noun)
• A branch of the U.S. Treasury Department concerned especially with protection of the President. (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.

• "By a system of secret service peculiar to these traders, the amount of the last offer is easily discovered, and the new bidder “sees that” (if I may be permitted to amuse myself with the phraseology of the Mississippi bluff-player) and “goes” a few ticals “better.”"
• "And then Silas Bannerman, a secret service agent of the United States, leaped into world-fame by arresting Emil Gluck."
• "On reaching Talgar, he set off into the hills on foot, followed by the NKVD secret service agents who tailed him everywhere, but they were local men, and Maclean ended up being entertained to lunch with them in a peasant cottage in the hills."