Cyanistes caeruleus, a small bird of the tit family Paridae, with an azure blue crown and dark blue line passing through the eye and encircling the white cheeks to the chin.

A species of North American jay with blue feathering from the top of its head to midway down its back, Cyanocitta cristata. / One of the blue-marked species of the Old World bird genus Coracias.

(UK, US, slang, chiefly in the plural) A policeman. / (UK, air force slang, dated) A member of the air force.

(astronomy) a very hot and very luminous star that emits visible light in the blue portion of the spectrum

(astronomy) a very large, hot and luminous star; a large blue giant

In cinema, a room with blue (or occasionally green) walls in which effects shots are filmed. / (aviation, slang) The toilet/washroom on a passenger aircraft.

(Australia) A blue-coated variety of the Australian Cattle Dog breed. / (Australia, slang) A police officer.

(informal) industrial action taken by members of the police, claiming sickness en masse.

A pair of trousers made from denim cotton and dyed dark blue.

(slang) a pornographic film