(biology) A form of aposematism in which a prey organism has conspicuous colors which function in deterring predators from consuming it.

A notice placed before the beginning of media content (usually an online article, e-mail, or post) to warn of potential traumatic triggers it contains.

A sign that indicates a danger, for example to vehicles on a road or of hazardous chemicals. / (figuratively) An indication that someone or something is in danger or at risk

(military) A warning, relatively far in advance, of a potential attack.

(attributive) Denoting equipment and systems designed to give sufficient warning of an impending event.

A bell rung to warn people of a danger. / (figuratively) A problematic or alarming aspect.

(meteorology) An indication that a tornado has been sighted in a viewing area.

(military) A warning of an ongoing or immediately impending attack.

(set phrase) A friendly warning of something undesirable.

A warning given too late to be useful.