blue [ME] The English blue and French bleu are ultimately the same word, which goes back to ancient Germanic and is related to the blae- in blaeberry [ME], a Scottish and northern English name for the bilberry [L16th]. Blue occurs in a number of phrases, in particular those relating either to depression and melancholy or to the blue of the sky, as in out of the blue, ‘as a total surprise’, a shortening of out of a clear blue sky [M19th]. See also bolt. Something occurring once in a blue moon [M19th] is something very rare. This has led to a new use [M20th] of blue moon for the rarely appearing second full moon in a calendar month.

Depression or melancholy have always been around, but no one called these feelings the blues until the mid 18th century, although people have been feeling blue since Late Middle English. The blues was a contraction of blue devils [E17th], which were originally baleful demons punishing sinners. In the 18th century people fancifully imagined them to be behind depression, and later also to be the apparitions seen by alcoholics in delirium tremens. The first printed record of the name of the melancholic music style is in the ‘Memphis Blues’ of 1912, by the American musician W. C. Handy, who later set up his own music-publishing house and transcribed many traditional blues. Its later development, rhythm and blues, appeared in the 1930s.

Obscene or smutty material has been known as blue since the mid 19th century. The link may be the blue gowns that prostitutes used to wear in prison, or the blue pencil traditionally used by censors. Blue-chip shares [L19th] are considered to be a reliable investment, though less secure than gilt-edged stock (used since the later 19th century for government stock, and earlier to suggest excellent quality). Blue chips are high-value counters used in the game of poker. In America a blue-collar worker [M20th] is someone who works in a manual trade, especially in industry, as opposed to a white-collar worker [E20th] in the cleaner environment of an office. A blueprint [L19th] gets its name from a process in which prints were composed of white lines on a blue ground or of blue lines on a white ground. See also murder.