/ Dictionary / Index S security thread: Meaning and Definition of Find definitions for: secu'rity thread" Pronunciation: [key] a colored thread running through the paper of a piece of paper money, used to deter counterfeiting. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. security risk secy Related Content Daily Word Quiz: perspicacious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language