noun
(countable and uncountable) The clear blue colour of the sky; also, a pigment or dye of this colour.
(heraldry) A blue colour on a coat of arms, represented in engraving by horizontal parallel lines.
(poetic) The unclouded sky; the blue vault above.
Any of various widely distributed lycaenid butterflies of the genus Celastrina.
Any of various Australasian lycaenid butterflies of the genus Ogyris.
Lapis lazuli.
adjective
Sky blue; resembling the clear blue colour of the unclouded sky.
Cloudless.
(heraldry) In blazon, of the colour blue.
verb
(transitive) To colour blue.