of the colour of a clear sky, between green and indigo in the spectrum
discoloured through cold, anger, bruising, or fear
bluish grey
a blue cat
having blue or patches of blue as a distinguishing feature
a blue tit
low in spirits
depressing or dismal
obscene or pornographic
a blue film
off-colour or risqué
blue jokes
Brit supporting the Conservative Party
once in a blue moon
very rarely
[originally in the sense ‘never’: the moon has a blue appearance when it is the second full moon in a month, which occurs occasionally.]until one is blue in the face
unsuccessfully for ever
You can complain until you're blue in the face but no one will listen
bluely adv
blueness noun
[Middle English from Old French blou, of Germanic origin]