c.1300,
bleu, blwe, etc., from O.Fr.
bleu, from Frank.
blao, from P.Gmc.
*blæwaz, from PIE base
*bhle-was "light-colored, blue, blond, yellow." "The exact color to which the Gmc. term applies varies in the older dialects; M.H.G.
bla is also "yellow," whereas the Scandinavian words may refer esp. to a deep, swarthy black, e.g. O.N.
blamaðr, N.Icel.
blamaður 'Negro' " [Buck]. Replaced O.E.
blaw, from the same PIE root, which also yielded L.
flavus "yellow," O.Sp.
blavo "yellowish-gray," Gk.
phalos "white," Welsh
blawr "gray," O.N.
bla "livid" (the meaning in
black and blue), showing the usual slippery definition of color words in I.E. The present spelling is since 16c., from Fr. influence. The color of constancy since Chaucer at least, but apparently for no deeper reason than the rhyme in
true blue (1500).
Blue (adj.) "lewd" is recorded from 1840; the sense connection is unclear, and is opposite to that in
blue laws (q.v.).
Blueprint is from 1886; the fig. sense of "detailed plan" is first attested 1926. For
blue ribbon, see
cordon bleu under
cordon. Blue moon emblematic of "very rarely" suggests something that, in fact, never happens (cf.
at the Greek calends), as in this couplet from 1528:
Yf they say the mone is blewe,
We must beleve that it is true.
Many IE languages seem to have had a word to describe the color of the sea, encompasing blue and green and gray; e.g. Ir.
glass (see
Chloe), O.E.
hæwen "blue, gray," related to
har (see
hoar), Serbo-Cr.
sinji "gray-blue, sea-green," Lith.
šyvas, Rus.
sivyj "gray."