3D Array?

Why does this not work?

myArray['numbers'] = array(1 => "One", 2 => "Two");
myArray['letters'] = array("A" => "Aye", "B" => "Bee");



???????

Any way to achieve something like that?

Sure, make myArray a variable. Right now its a constant. It'll work fine after that.
It is only a 2 dimensional array though, not a three.