/ Dictionary / Index F flag day: Meaning and Definition of Find definitions for: flag' day" Pronunciation: [key] — Brit. (sometimes caps.)Brit. See Flag' Day" Pronunciation: [key] June 14, the anniversary of the day (June 14, 1777) when Congress adopted the Stars and Stripes as the national flag of the United States. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. flag flagella Related Content Daily Word Quiz: belligerent Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language