I recently started playing Words With Friends again on my phone. One thing I don’t understand – does it use dictionary.com as it’s official dictionary or not? If you use the dictionary function to look up a word that’s been played, it looks like it is referencing dictionary.com. But there have been several times I have tried to play a word, and it tells me the word is not valid, so I go look it up on dictionary.com and there it is! So what’s the deal?
Dictionary.com republishes definitions from other dictionaries, primarily Random House, but also Collins, etc.
So the answer is “probably,” but indirectly.
Similarly, IIRC, the Official Scrabble Dictionary just draws from a list of standard dictionaries, and includes any word that shows up in at least two of those standard dictionaries. Though that’s just for tournaments: The actual rules of the game say nothing about what dictionary is to be used, beyond that all of the players need to agree on it before the start of the game.
Ahem. :dubious:
Posted from my phone. I blame autocorrect. 
The other odd thing I’ve noticed when checking the dictionary in WWF is that no matter how obscure the word is, it never seems to be more than a couple of ticks from the “common” end of the spectrum.