Other than the Official Scrabble Players Dictionary, what dictionary carries this word?
Hardly the most authoritative source, but I just found it in thefreedictionary.com.
I don’t know, I’d consider American Heritage, Collins, and Random House to be a pretty good consensus.
I have three dictionaries on my end table: American Heritage College (3rd edition), Webster’s New World (3rd college edition), and the compact OED. They all have “ai” meaning “sloth”. So my guess is “most of them”.
There are plenty of lists of acceptable two-letter words in Scrabble.
The Century Dictionary published way back around 1890 included this definition.
The OED, in the A-B volume originally published in the 1880s, had the word, with the first quotation from 1693.
Thanks, all. Apparently the editors of Merriam-Webster are a little more conservative. I just picked this one for the question, but there are a number of Scrabble words not found in it.
I think the standard used by the official Scrabble dictionary is that they have a library of five or six reputable dictionaries, and consider a word “real” if it appears in at least two of them, or something like that.
Incidentally, the rules of the game itself don’t actually specify a dictionary to use, and just say that the players should agree to one before the game starts.
Onelook Dictionary Search finds “ai” in 92 different online dictionaries (although not always in meaning of a type of sloth, and, in some cases, as an initialism rather than a word).
You’re talking about friendly games of Scrabble, where normal people can use any dictionary they have in the house. And while playing, they might also hold a friendly conversation, drink a cup of coffee, and enjoy themselves, seated around the kitchen table…
But there’s also “non-friendly” Scrabble. 
Some people take their Scrabble SERIOUSLY. They play in tournaments with cuthroat competition; dozens of people seated at tables in dead silence, with frowning faces, and following rigid rules of ettiquette.
And they don’t just use any old dictionary…they use the sacred OWL–official word list. Which can be bought in book form, but, like the Koran, must be handled only while wearing white gloves.
Yes, because that’s the dictionary those players have agreed to use. It’s a perfectly valid choice, and it’s a very common one, but it is not the only valid choice. There are also cutthroat Scrabble players (like, say, my aunts-- Nobody who had ever seen my family play would mistake it for “friendly”) who use as their dictionary “That old tome that Grandma keeps in her nightstand bookshelf”. Which is also valid and in perfect accordance with the rules.
My Webster’s New Collegiate Dictionary, published by Merriam-Webster, considers ‘ai’ a perfectly cromulent word.
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Ai \A"i\, n.; pl. {Ais}. [Braz. a["i], ha["i], from the animal's
cry: cf. F. a["i].] (Zool.)
The three-toed sloth ({Bradypus tridactylus}) of South
America. See {Sloth}.
[1913 Webster] Aiblins
From WordNet (r) 3.0 (2006) [wn]:
AI
n 1: an agency of the United States Army responsible for
providing timely and relevant and accurate and synchronized
intelligence to tactical and operational and strategic
level commanders [syn: {Army Intelligence}, {AI}]
2: the branch of computer science that deal with writing
computer programs that can solve problems creatively;
"workers in AI hope to imitate or duplicate intelligence in
computers and robots" [syn: {artificial intelligence}, {AI}]
3: a sloth that has three long claws on each forefoot and each
hindfoot [syn: {three-toed sloth}, {ai}, {Bradypus
tridactylus}]
4: the introduction of semen into the oviduct or uterus by some
means other than sexual intercourse [syn: {artificial
insemination}, {AI}]
1913 Webster means the 1913 edition of Webster’s Revised Unabridged Dictionary, so it was in use over a century ago at least.
Hmmm. . . My latest one is from 2002, and it’s in there only in all-caps meaning “Artificial Intelligence.”
I used a Webster’s New Collegiate Dictionary as a handy reference when reading in bed, and it let me down many times. My American Heritage Unabridged usually came through, but thank goodness now for the one built into my Nook (which seems far better than the Webster’s), and for the web, when that fails.
I wish my e-reader had a feature to remember every word I look up and keep them all in a list. As it is, I’m trying to get into the habit to highlight any word I look up, so I can review later. Neal Stevenson’s Cryptonomicon had me look up quite a few, maybe as many as ten. Oscar Wilde also used a few I’d never seen.
Yes, but is “cromulent” in there?
Your dictionary is almost old enough to drive, dude. The Official Scrabble Dictionary uses M-W, so a more recent version should have what you need.
Maybe when they embiggen the dictionary for the next edition.