One of the mysteries of the English language finally explained.
A person or thing acting as a danger signal; (sometimes) specifically an animal or plant whose population size, state of health, etc., is viewed as indicative of the state of the environment.
1980s; earliest use found in The Washington Post. With allusion to the practice of keeping domestic canaries in coal mines to indicate the build-up of gases.
In this article we explore how to impress employers with a spot-on CV.