6. Blue Moon
If you want to indicate that something happens rarely, then you might use the phrase once in a blue moon. In an extremely rare case, the moon might actually look blue after a volcanic eruption because of the dust particles in the air, (19) but that likely isn't the origin of the expression. This phrase goes as far back as Medieval England and originally meant impossible, as in when pigs fly. Nowadays, on the other hand, the term blue moon describes a real—and rare—astronomical phenomenon, and once in a blue moon has had the meaning rare since around 1821. (19) There are actually two scientific definitions of a blue moon. First, there are four astronomical seasons: spring, summer, fall, and winter, and each season normally has three full moons. When there is a fourth full moon in one season, the third moon that season is called a blue moon, and according to timeanddate.com, (20) this is the correct definition. The second definition of blue moon is a second full moon in one month. Whichever meaning you wish to use, a blue moon will not happen often. According to the first definition on timeanddate.com, there will be blue moons in May 2016, May 2018, August 2021, and August 2024; according to the second, blue moons will occur in January and March 2018 and in October 2020.
7. Blue Movie
The seventh meaning of blue is pornographic, as in the phrase blue movie. The word blue has meant obscene since the 1820s, (21) and Dictionary.com's 17th definition of blue is “marked by blasphemy.” (22) The origins of this association with the color blue are murky. Two theories (21) are that it is related to the blue gowns that ladies of the night were made to wear when imprisoned, and that certain undesirable French books were bound in blue paper covers. Another phrase associated with off-color language is blue humor, which refers to dirty jokes. (23) Comedians such as Andrew Dice Clay are known for this kind of comedy.
8. Blue Laws
It's interesting that the next meaning of blue is the polar opposite of what we just said, in this case puritanical. (24) The term blue laws refers to state or local laws that prohibit certain activities on Sundays, and many of these laws came about because of religious ideals. (25) For example, some blue laws prevented stores from being open, did not permit merchants or laborers to work, and prohibited the sale of liquor and tobacco on Sundays. Some blue laws are still in force. The origin of the term is unclear. (26) One theory is that it comes from the color of the paper on which these laws were written, but that does not seem to be true. Perhaps it is related to the term bluenose, which means a puritanical person. (27)
9. Feeling Blue
Two more meanings of blue to go. The next to last meaning is perhaps the most common connotation: When you're feeling blue, you're sad. This melancholy meaning of blue has been around since 1385, when Chaucer used the term. (28) A related idiom is in a blue funk. (29) Some people suffer from seasonal affective disorder, appropriately abbreviated SAD, where sufferers start being depressed around fall, and the feeling continues through the winter. (30) These people might experience what's known as a blue Christmas, a sad Christmas, (31) and Elvis sang a song with this title. (32) We hope that this holiday season is joyful for you instead of blue.
10. Blue Hanukkah
Which brings us to our last tidbit about the color blue. This color, along with the color white, is widely associated with the Jewish holiday Hanukkah. The reason might seem obvious to those who know that the Israeli flag is blue and white. This flag was designed in 1891 and adopted in 1948. (33) The flag's stripes are blue because they represent the blue thread that the Torah commands be used on the fringe of the prayer shawl known as a tzitzit. (34) The dye that makes the thread blue comes from a shellfish that lives in the Mediterranean Sea. (34)
We hope that you've enjoyed this colorful episode. Happy Holidays!
[Correction Note: This article originally said that a blue moon is the fourth full moon in a season instead of the third full moon in a season that has four.]