Thomas T. Frost Apr 28, 2022:

Case Tony, wherever I look on their website, it's written Airbnb (or airbnb a few places), but that doesn't preclude, of course, that you have seen them use AirBnB somewhere. Here is what my New Oxford Style Manual has to say about plurals and apostrophes:

'The apostrophe may be used when clarity calls for it, for example when letters or symbols are referred to as objects:
- dot the i's and cross the t's
- find all the number 7's
- she can't tell her M's from her N's
Such items may also be italicized or set in quotes, with the s set in roman outside any closing quote:
- subtract all the xs from the ys
- subtract all the 'x's from the 'y's

This ‘rule’ leaves some discretion to the writer, but there seems to be various slightly different ‘rules’ about the use of apostrophes for plurals.

Tony M Apr 28, 2022:

@ Thomas Whether or not it is written as one word, AirBnB themselves do indeed used mixed case, and the 'BnB' part is a very clear abbreviation of the EN expression 'Bed and Breakfast' — so I think the rule still holds good.

AllegroTrans Apr 27, 2022:

I humbly stand corrected! Tony, Thomas, you are right. It looks wrong to me, but Googling tells me it's correct and not a "grocer's apostrophe" as I first thought. Hope this blunder doesn't get me exeplled from the Society...

Thomas T. Frost Apr 27, 2022:

In this case In this case, it's about the company name Airbnb (or rather the company's hosts), which is not written in two words, and which is not written with mixed uppercase and lowercase letters by the company itself, so although the second half of the company name is based on an abbreviation, it's a bit of a stretch to slice the company name in two and call the second half an abbreviation. It's a proper noun.

But the plural of a single letter requires an apostrophe: there are three i's in 'Mississippi'.

Tony M Apr 27, 2022:

@ A/T Actually, that's not quite true!
In this case, it is perfectly correct: when making the plural of an abbreviation like 'BnB', the apostrophe should be used if (and only if) the abbreviation contains mixed caps and l/c letters.

AllegroTrans Apr 27, 2022:

DANGER: Message from the Apostrophe Society Appalling misuse of the apostrophe. It is NEVER used to make a plural, neither in a noun or in an abbreviation