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a piece of cloth with a special coloured design on it that may be the symbol of a particular country or organization, may be used to give a signal or may have a particular meaning. A flag can be attached to a pole (= a long thin straight piece of wood or metal) or held in the hand. 旗 
the Italian flag 意大利国旗 the flag of Italy 意大利国旗 The hotel flies the European Union flag. 这家旅馆悬挂着欧盟的旗帜。 The American flag was flying. 美国国旗飘扬。 Hundreds of people cheered and waved flags. 数百人欢呼并挥舞旗帜。 All the flags were at half mast (= in honour of a famous person who has died). 到处都下半旗致哀。 The black and white flag went down, and the race began. 黑白旗落下，赛跑开始了。 The assistant referee had raised his flag for offside. 助理裁判举起了越位的旗子。 A large Brazilian flag fluttered above the podium. 讲台上飘扬着一面巨大的巴西国旗。 His shot went closer to the corner flag than the goal. 他的射门比球门更靠近角旗。 Australia's flag bearer (= person who carried the flag) at the Sydney Olympics 悉尼奥运会上澳大利亚的旗手
Extra ExamplesTopics Sports: ball and racket sportsb1A tattered flag hung from the roof of the burnt-out building. 一面破旗挂在烧毁的建筑物房顶上。 The crowd all waved flags as the president came past. 总统经过时，人群中每个人都挥动着旗帜。 The fact that it was so cheap should have been a warning flag for me. 这东西这么便宜，早就应该引起我的警惕了。 a flag fluttering in the breeze 微风中飘扬的旗帜 a flag of truce 休战旗
Oxford Collocations Dictionaryadjective- national
- battle
- burning
- …
- fly
- hang
- hang out
- …
- hang
- flap
- flutter
- …
- pole
- under a/the flag
- flag of
- flag of convenience
- flag of surrender
used to refer to a particular country or organization and its beliefs and values 旗帜（指某国家或组织及其信仰和价值观） to swear allegiance to the flag 面对旗帜作效忠宣誓 - under a flag
The team competed under the Olympic flag. 该队在奥林匹克旗帜下比赛。 - under the flag of something
He was working under the flag of the United Nations. 他在联合国工作。
a flower that is a type of iris and that grows near water 菖蒲；鸢尾；香蒲 yellow flags 黄菖蒲
- (also flagstone)
a large flat square piece of stone that is used for floors, paths, etc. （体育运动的）信号旗，标志旗
Word Originnoun senses 1 to 3 mid 16th cent.: perhaps from obsolete flag ‘drooping’, of unknown ultimate origin. noun sense 5 late Middle English (also in the sense ‘turf, sod’): probably of Scandinavian origin and related to Icelandic flag ‘spot from which a sod has been cut’ and Old Norse flaga ‘slab of stone’. noun sense 4 late Middle English: related to Middle Dutch flag and Danish flæg; of unknown ultimate origin.
Idioms
fly/show/wave the flag
to show your support for your country, an organization or an idea to encourage or persuade others to do the same 表示并号召拥护自己的国家（或某组织、某思想）
keep the flag flying
like waving a red flag in front of a bull (US English)
(British English a red rag to a bull)
something that is likely to make somebody very angry 斗牛的红布；激起人怒火的事物