The colour of the clear sky or the deep sea, between green and violet in the visible spectrum, and one of the primary additive colours for transmitted light; the colour obtained by subtracting red and green from white light using magenta and cyan filters; or any colour resembling this.

A blue dye or pigment.

Any of several processes to protect metal against rust.

Blue clothing

(in the plural) A blue uniform. See blues.

A member of law enforcement

The sky, literally or figuratively.

The ocean; deep waters.

The far distance; a remote or distant place.

Anything blue, especially to distinguish it from similar objects differing only in color.

A dog or cat with a slaty gray coat.

One of the colour balls used in snooker, with a value of five points.

Any of the butterflies of the subfamily Polyommatinae in the family Lycaenidae, most of which have blue on their wings.

A bluefish.

An argument.

A liquid with an intense blue colour, added to a laundry wash to prevent yellowing of white clothes.

A type of firecracker.

A bluestocking.

One of the three color charges for quarks.

To make or become blue.

To treat the surface of steel so that it is passivated chemically and becomes more resistant to rust.

(laundry) To brighten by treating with blue (laundry aid)

To spend (money) extravagantly; to blow.

Of the colour blue.

Depressed, melancholic, sad.

Pale, without redness or glare; said of a flame.

Supportive of, run by (a member of), pertaining to, or dominated by a political party represented by the colour blue.

Of the higher-frequency region of the part of the electromagnetic spectrum which is relevant in the specific observation.

(of steak) Extra rare; left very raw and cold.

(of a dog or cat) Having a coat of fur of a slaty gray shade.

Severe or overly strict in morals; gloomy.

(of women) literary; bluestockinged.

Having a color charge of blue.

(entertainment) Risque or obscene