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You know there are some keywords in AppleScript, huh? Such as "launch", "tell", "and" or "word"... For a complete list of keywords in AppleScript, you can navigate (under OS X) to /System/Library/Components/AppleScript.component/Resources folder and open "AppleScript.rsrc" using a resource-fork editor, such as Resorcerer.
You are looking for the resource "aeut", which contains all this info. If you duplicate the file to a new location, you can change "aeut" to "aete" and save, so you can browse the dictionary as usually in a script editor such as Smile or Script Debugger (actually there are some bugs in the dictionary-reader of Apple's Script Editor).
NOTE that this is only an informative list of commands and classes. Not all of them are supported nor implemented in the AppleScript language (that's because it's hidden). For example, the class "arc" will only work in applications that have implemented the QuickDraw Graphics Suite. So, treat it as a curiosity, not as documentation.