As for dictionaries, mobile phones and apps changed everything. However, before these 'advances' the dictionary to use was the correct Scrabble one.
What I liked about the proper Scrabble dictionary was that none of the words were explained. So you could play words beyond your normal level of spoken English without knowing what they meant, but you would know they were in the proper Scrabble dictionary. So you could have 'ax' and not know what it meant or extend it on the next go to 'axon' with no idea what that meant. You did know from previous games that this was legit and that was all that mattered.
To people not in the game this dictionary seemed absurd. The language had morphed into code. A code that you had to know if you were ever to have a chance of using complete 7 letter 'laydowns' several times in a game and do those cool two letter joins to make such things possible.
Most of the hardcore Scrabble people I've known would object to that. ("This isn't 'Nam, there are rules.")
At a beginner level, it's more fun when no one knows the word list perfectly, and you shouldn't allow it.
At a slightly-above-beginner level, say where one player knows the two-letter words and others do not, knowing the two-letter words is such a huge advantage that it's a sensible house rule to level the playing field a little, and likely make it more fun for both.
No, this is against the rules. You know what we call a list of words? A dictionary. You aren't allowed to have those open until a word gets challenged. A decade ago I had all the two letter words in the Scrabble dictionary memorized, I doubt I'd still be able to spit them all out.
> No, this is against the rules.
It wasn't, but even if it was, that's only the official rules. We can choose to play by different rules.