union jack

noun

1. a jack consisting of the union of a national flag or ensign, as the U.S. jack, which has the white stars and blue field of the union of the U.S. national flag.

2. (often initial capital letter),  the British national flag.

3. any flag the overall design of which is a union.

Union Jack

noun

1. a common name for Union flag

2. (often not capitals) a national flag flown at the jackstaff of a vessel

Word History and Origins

Origin of union jack¹

First recorded in 1665–75