Red flag

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Red flag is an idiom that may be used as a noun or a verb, in which case the expression is hyphenated. We will examine the meaning of the idiomatic phrase red flag, where it came from, and some examples of its use in sentences.

The noun red flag, when used as an idiom, means a warning, a clue that there may be a problem, a sign of danger. The verb red-flag means to identify something as a sign of danger, to label something as a warning. Related words are red-flags, red-flagged, red-flagging. Note that the verb form takes a hyphen. A red flag was used in the 1600s to signal that an army was ready to go into battle. By the 1700s, red flag came into use as an idiom to mean a warning sign. Literal, physical red flags are used as a sign of warning in many circumstances. Red flags are used in sports, as a sign of wildfire hazard, as a train signal, as a rank of terrorist threat, and in many, many other ways. In all cases, the red flag is a warning of danger.


It’s the third year Handy has tried to push a “red-flag” bill — or legislation that would enable a family member or someone from law enforcement to request a court strip a firearm from a person in crisis, either in danger to themselves or others. (The Deseret News)

Delta, American, and United just suspended all China flights, a red flag as the unprecedented coronavirus wreaks havoc on the airline industry (Business Insider)

He alleged that Low with the help of other unauthorised third parties, had made 20 transactions to regularise the accounts totalling RM12 million through several local and foreign remittances of funds and that the accounts had been ‘red-flagged’ by Bank Negara Malaysia (BNM). (The Borneo Post)