Actionscript 3.0 :: Optimization Of HUGE List Comparison: Dictionary?

I'm on the brink of finishing the first iteration of my first game ever o/ and of course the last item I need to complete is the hardest. I am making a simple word game, and all details aside, the task at hand is a conditional block to determine whether the word the user has entered is real, and in order to do this I need to somehow compare it to a dictionary list.

1 hour of research has quickly opened up an entire universe of data structures, open source xml documents, people willing to take my money for spell checkers, and of course RegExp which I have no experience using (but am willing, and wanting, to learn!). One of the main problems Google is giving me is the addition of the Dictionary class in AS3, which "lets you create a dynamic collection of properties, which uses strict equality (===) for key comparison on non-primitive object keys..." So finding previous literal dictionary uses is tough.

I soon found taking a dictionary txt file (118619 lines) and converting it line by line into an array takes 3 minutes on my beast of a laptop gaming rig (Asus W90), and while I knew this was a bad idea, it was a nice learning experience (to give me a gauge of processing abilities).

I am wondering whether using XML is an appropriate alternative, or if there is a way to externally access a dictionary somewhere online. Looking at the XMLList Class available I see text() and toString() methods; yet I still see heavy iterations in accessing the dictionary.

Which brings up the next point: easiest way to find a String match. I understand that comparing each word one by one would be tedious for the program, so maybe splitting up the list by letter (or maybe string length, looking at the file), or first and last letter.