'Red flag' definitions:

Definition of 'red flag'

From: WordNet
noun
A flag that serves as a warning signal; "we didn't swim at the beach because the red flag was up"
noun
The emblem of socialist revolution
noun
Something that irritates or demands immediate action; "doing that is like waving a red flag in front of a bull"

Definition of 'Red flag'

From: GCIDE
  • Flag \Flag\, n. [Cf. LG. & G. flagge, Sw. flagg, Dan. flag, D. vlag. See Flag to hang loose.]
  • 1. That which flags or hangs down loosely. [1913 Webster]
  • 2. A cloth usually bearing a device or devices and used to indicate nationality, party, etc., or to give or ask information; -- commonly attached to a staff to be waved by the wind; a standard; a banner; an ensign; the colors; as, the national flag; a military or a naval flag. [1913 Webster]
  • 3. (Zool.) (a) A group of feathers on the lower part of the legs of certain hawks, owls, etc. (b) A group of elongated wing feathers in certain hawks. (c) The bushy tail of a dog, as of a setter. [1913 Webster]
  • 4. (Zool.) One of the wing feathers next the body of a bird; -- called also flag feather. [Webster 1913 Suppl.]
  • Black flag. See under Black.
  • Flag captain, Flag leutenant, etc., special officers attached to the flagship, as aids to the flag officer.
  • Flag officer, the commander of a fleet or squadron; an admiral, or commodore.
  • Flag of truse, a white flag carried or displayed to an enemy, as an invitation to conference, or for the purpose of making some communication not hostile.
  • Flag share, the flag officer's share of prize money.
  • Flag station (Railroad), a station at which trains do not stop unless signaled to do so, by a flag hung out or waved.
  • National flag, a flag of a particular country, on which some national emblem or device, is emblazoned.
  • Red flag, a flag of a red color, displayed as a signal of danger or token of defiance; the emblem of anarchists.
  • To dip, the flag, to mlower it and quickly restore it to its place; -- done as a mark of respect.
  • To hang out the white flag, to ask truce or quarter, or, in some cases, to manifest a friendly design by exhibiting a white flag.
  • To hang the flag half-mast high or {To hang the flag half-staff} or To hang the flag at half-staff, to raise it only half way to the mast or staff, as a token or sign of mourning.
  • To strike the flag or To lower the flag, to haul it down, in token of respect, submission, or, in an engagement, of surrender.
  • Yellow flag, the quarantine flag of all nations; also carried at a vessel's fore, to denote that an infectious disease is on board. [1913 Webster]

Synonyms of 'red flag'

From: Moby Thesaurus