From Longman Dictionary of Contemporary EnglishUnion JackˌUnion ˈJack noun [countable] PGthe national flag of the United Kingdom
Examples from the Corpus
Union Jack• Christie, as you saw when he walked slowly round the track in a Union Jack, loves a wallow in praise.• A Union Jack was to be purchased for the occasion at a cost not exceeding one pound.• A small Union Jack was hanging from a pole.• Disloyal Catholics did not fly the Union Jack.• You put the Union Jack behind them in the picture and you state, Our home-grown Brit boys'.• When the women reached the pole they raised the Union Jack, sang the national anthem and drank champagne.• It was, Robert noted with a mixture of horror and relief, the Union jack.Origin Union Jack (1600-1700) jack “flag” ((17-20 centuries)) 