a nautical term for a blue flag having a white square in the center, hoisted at the fore royal masthead as a signal to report on board as the vessel is about to go to sea, attested by c. 1800, from blue (adj.1), but the significance of peter is uncertain and disputed. Two common guesses are that it is an abbreviation of repeater or that it stands for French partir.
1904 in reference to the high-value poker counter, also in the figurative sense of "valuable." The stock exchange sense, in reference to "shares considered a reliable investment," is recorded by 1929; especially of stocks that saw spectacular rises in value in the four years or so before the Wall Street crash of that year wiped out most of it. See blue (adj.1) + chip (n.1).
1809 in reference to the blood that flows in the veins of the old and aristocratic families of Spain, translating Spanish sangre azul, claimed by certain families of Castile that held themselves uncontaminated by Moorish or Jewish admixture; the term probably is from the notion of the visible veins of people of fair complexion. In reference to English families by 1827. As a noun, "member of an old and aristocratic family," by 1877. See blue (adj.1) + blood (n.).
"a long time," 1821, often in phrases indicating something rarely occurring. Compare at the Greek calends (from an ancient Roman phrase alluding to the fact that the Greeks had nothing corresponding to the Roman calends), and the native in the reign of Queen Dick and Saint Geoffrey's Day "Never, there being no saint of that name," reported in Grose (1788). Nevermass "date which never comes" is from 1540s. Blue moon is suggested earliest in this couplet from 1528:
Yf they say the mone is blewe,
We must beleve that it is true.
Though this might refer to calendrical calculations by the Church. Thus the general "rareness" sense of the term is difficult to disentangle from the specific calendrical one (commonly misinterpreted as "second full moon in a calendar month," but actually a quarterly calculation). In either case, the sense of blue here is obscure. Literal blue moons do sometimes occur under extreme atmospheric conditions.
severe Puritanical code said to have been enacted mid-17c. at the founding of New Haven and Connecticut colonies, 1781; of uncertain signification, perhaps from the notion of coldness, or from one of the figurative senses in blue (adj.1). Blue was the color adopted by 17c. Scottish Covenanters (in contradistinction to the royal red) and hence the color for a time acquired an association with strictness in morals or religion. Or perhaps connected to bluestocking in the sense of "puritanically plain or mean" (see bluestocking, which is a different application of the same term); the parliament of 1653 was derisively called the bluestocking parliament.
The assertion by some writers of the existence of the blue laws has no other basis than the adoption by the first authorities of the New Haven colony of the Scriptures as their code of law and government, and their strict application of Mosaic principles. [Century Dictionary]
Long, detailed lists of them often are given, but the original reference (in an anonymous history of Connecticut printed in London during the Revolution) says they were so-called by the neighboring colonies, "were never suffered to be printed," and then gives its own long list of them in quotations. The common explanation (dating to 1788) that they were written on blue paper is not now considered valid.
"substance which makes (something) blue," 1660s, verbal noun from blue (v.).
"depression, low spirits," 1741, from blue (adj.1) in the sense "low-spirited" (c. 1400).