(idiomatic) Something whose sensitivity to adverse conditions makes it a useful early indicator of such conditions; something which warns of the coming of greater danger or trouble by a deterioration in its health or welfare.

(idiomatic) To call to task or to reprimand severely.

Alternative form of canary in a coal mine

plural of canary in the coal mine

plural of canary in a coal mine

Alternative form of carry coals to Newcastle

(military, slang) a style of soldier's helmet that looks the same as or similar to the helmet used by current Chilean soldiery, German soldiery at the end of WWI and during WWII, and Chinese soldiery during the Second Sino-Japanese War

plural of coal scuttle helmet

plural of coal-scuttle bonnet

(historical) A kind of woman's bonnet, shaped like an inverted coal scuttle.