Q: Should the title of a holiday song be “Christmas PJs,” “Christmas PJ’s,” or “Christmas Pj’s”?
A: We’d use two capital letters without an apostrophe in writing the abbreviation of “pajamas.” So our recommendation is “Christmas PJs” for the song title.
We’re treating “PJ” here as an initialism, an abbreviation that’s spoken as letters, like “IQ” for “intelligence quotient” or “ICBM” for “intercontinental ballistic missile.” When we pluralize those, we simply add an “s” at the end: “IQs” and “ICBMs.”
Although most initialisms consist of the first letter or letters of words in a phrase, some are made up of selected letters in a single word, such as “KO” for “knockout” and “TV” for “television.” When we pluralize them, we also add just an “s”: “KOs,” “TVs.” Similarly, the plural of “PJ” would be “PJs” (pronounced PEE-jays).
That’s what we would do, and we’ll explain why later. But first we should mention that this is a matter of style, not correctness. Although publishers generally do it our way, the 10 online standard dictionaries we usually consult are all over the place in capitalizing and punctuating the abbreviation of “pajamas” (spelled “pyjamas” in the UK).
Cambridge and Lexico (the former Oxford Dictionaries Online) spell it “PJs” while Merriam-Webster and Merriam-Webster Unabridged spell it “pj’s.” American Heritage gives three separate spellings: “PJs or PJ’s or pj’s” (“or” indicates equal variants).
Here are other entries: Collins, “PJs or pj’s”; Dictionary.com (based on Random House Unabridged), “p.j.’s or P.J.’s”; Longman, “pj’s, PJ’s” (the comma indicates equal variants); Macmillan and Webster’s New World, “pj’s.”
Although you could defend any of those spellings by citing a standard dictionary, we still prefer two capital letters and no apostrophe: “PJs.” In the new fourth edition of Woe Is I, Pat gives her recommendations on pluralizing abbreviations:
Over the years, authorities have disagreed on how we should form the plurals of abbreviations (GI, rpm, RBI), letters (x, y, z), and numbers (9, 10). Should we add s, or ’s ? Where one style maven saw UFO’s, another saw UFOs. One was nostalgic for the 1990’s, the other for the 1990s.
The problem with adding ’s is that we get plurals and possessives confused. Is UFO’s, for example, a plural (I see two UFO’s) or a possessive (That UFO’s lights are violet)?
Here’s what I recommend, and what most publishers do these days. To form the plurals of abbreviations and numbers, add s alone, but to form the plural of a single letter, add ’s. CPAs, who know the three R’s and can add columns of 9s in their heads, have been advising MDs since the 1980s to dot their i’s, cross their t’s, and never accept IOUs. Things could be worse: there could be two IRSs.
Why use the apostrophe with a single letter? Because without it, the plural is often impossible to read. Like this: The choreographer’s name is full of as, is, and us. (Translation: His name is full of a’s, i’s, and u’s.)”
As for the etymology, English borrowed “pajamas” at the beginning of the 19th century from Urdu, adding a plural “s” to the South Asian term pāy-jāma or pā-jāma, according to the Oxford English Dictionary. Urdu got the word from Persian, the OED says, where pāy or pā meant “foot” or “leg,” and jāma “clothing” or “garment.”
The dictionary says the term originally referred to “loose trousers, usually of silk or cotton, tied round the waist, and worn by both sexes in some Asian and Middle Eastern countries.” As Oxford explains, “The loose trousers were adopted by Europeans living in Eastern countries, esp. for night wear, and the word came to be applied outside Asia (originally in trade use) to a sleeping suit of loose trousers and jacket.”
The OED’s earliest citation is from an 1800 memo about the wardrobe of the ruler of the Kingdom of Mysore in southern India: “Memorandum relative to Tippoo Sultaun’s wardrobe … 3d, pai jamahs, or drawers” (published in The Asiatic Annual Register, 1801).
Interestingly, “pajamas,” the preferred American spelling, showed up before “pyjamas,” the British preference, according to OED citations: “He usually undresses, puts on his pajamas (the loose Turkish trouser).” From The Hand-Book of India, by Joachim Hayward Stocqueler, London, 1844.
The “y” spelling first appeared more than three decades later: “I relinquished my English chemise de nuit and took to pyjamas—bedclothes are not used at this time of year [in Japan].” From a Sept. 6, 1878, diary entry in Round the World in Six Months (1879), by Edward Smith Bridges.
The OED’s earliest example for the abbreviated version is in a 1930 letter from a new cadet at West Point to his parents: “Shirts, sheets, P.J.s, sox, etc.” From Cradle of Valor: The Intimate Letters of a Plebe at West Point Between the Two World Wars (1988), by Dale O. Smith.
The next citation is from a caption in the New Yorker (March 12, 1949): “Toothpaste, check; change of linen, check; pj’s, check.” And the third is from Saul Bellow’s novel Herzog (1964): “Put on those p-j’s now.”
And the most recent cite is from the January 2002 issue of B magazine: “I’d arranged to meet Matt for lunch at 1pm, but was still in my PJs at 12.45pm. He ended up waiting an hour.”