blue

The word “blue” means having the colour of a clear daytime sky. In plain terms, the colour blue, or — informally — a low, sad mood.

“Blue” is pronounced bloo (/bluː/ in IPA).

Here is “blue” used in a sentence: “She painted the nursery walls a soft blue.”

Words with a similar meaning to “blue” include azure, cerulean, navy, sapphire, X-rated and indigo.

The opposite of “blue” — its antonyms — are nonblue, unblue, conservative, red and Republican.

Depending on how it is used, “blue” can be an adjective and a noun.

The word “blue” comes from Latin. From Old French bleu, from a Frankish word related to Proto-Germanic *blēwaz ("blue, dark blue"); a distant cousin of Latin flavus ("yellow") and doublet of the English word "blow.".

“Blue” is a very common word in modern English, usually learned at around the A1 level.

Sunlight contains all colours, and as it passes through the atmosphere, air molecules scatter the shorter blue wavelengths far more than the longer red ones. That scattered blue light reaches our eyes from all over the sky, which is why a clear daytime sky, and the colour named after it, appears blue.

Feeling blue is an informal expression meaning sad, low, or mildly down. The colour blue has long been linked with melancholy in English, giving us phrases like "the blues." So describing someone as blue usually refers to their mood, not their appearance, a gentle way of saying they are unhappy.

Blue is a primary colour, so in traditional paint mixing it cannot be made by combining other colours. Instead, blue is one of the base colours used to mix others: blend it with yellow for green, or with red for purple. In light, blue is also a primary, alongside red and green.

Blue ranges widely, from pale sky blue and baby blue through to navy, royal blue, and midnight blue. Named shades include azure, cobalt, teal, turquoise, and cerulean. They differ in lightness and in how much green or purple they contain, giving everything from icy pastels to deep, near-black tones.