A definition for the word "flag" (in English) actually caused the editors of the DoV more problems than any other. In the end we decided to go with a completely generic, non-exclusive definition, and that it was far more useful to detail flags by their type and/or usage — hence the single definition under FLAG, and multiple definitions under BANNER, ENSIGN, STANDARD, COLOUR etc., etc. As just one example, we are saying that a banner of arms (or armorial banner if you prefer) may — if you so wish of course — be generically defined as a flag, but is more specifically detailed under "banner ¹⁾".
Christopher Southworth, 12 Aug 2007

But "flag" also means flat pieces of stone paving a garden pathway, a type of iris growing in that garden, and, as a verb, to become weary and tired! Not to mention several meanings that derive directly from our favorite “vex-ation”, like «flagging a message» and «flagging a taxicab» — meaning «to put a vexillological but metaphorical flag up as a signal».
Bill Dunning, 11 Aug 2007

To flag down a vehicle

London hackney carriage (taxi) cabs used to have a red flag, made out of metal, which was a part of the meter, to determine the fare and visible from the outside of the taxicab, so that potential passengers could see that the taxi was available for hire. When the passenger got into the cab, the driver would put the flag down. You can still see this in the 1963 classic film of its genre, Carry on, Cabbie. These days, it is symbolic rather than literal, which probably accounts for the diminishing use of the phrase in The Queen’s English.
Colin Dobson, 11 Aug 2007

So "flag down a hack" means literally to cause the flag to be turned down, even if it’s only a remembered symbolic flag.
Bill Dunning, 12 Aug 2007

I don’t think so: There it likely is referring to how sometimes (warning a train, for example), you actually wave a flag at a vehicle. The word "flag", I think, was also used in the United States, but I think it was just a lever. Usage of the word "flag" may have crossed over without the actually symbolism — open cabs here have lights on top.
Nathan Lamm, 12 Aug 2007

[⚓]

Word " flags "

Word:: flags
Script:: Latin
Variant:: plural of "flag"

(See 1 other wordform identical to this.)

[⚓]

Word " 𐑓𐑤𐑨𐑜 "

Word:: 𐑓𐑤𐑨𐑜
Transliteration:: flæg
Script:: Shavian
Variant:: less common orthography form of "flag"

[⚓]

Word " 𐑁𐑊𐐰𐑀 "

Word:: 𐑁𐑊𐐰𐑀
Transliteration:: flăg
Script:: Deseret
Variant:: historical/residual form of "flag"
Remarks:: Deseret (Utah), mid 1800ies

[⚓]

Word "  "

Word:: 
Transliteration:: flæg
Script:: Visible Speech
Variant:: historical/residual form of "flag"
Remarks:: 1880s experimental use in education for the deaf in North America. CSUR encoding, looks like "ɜωᒐ̄⋴"