Yes, it really is a word.
It's a word that's not used much anymore. If you know what "Paradox" means, then you pretty much know what "Antinomy" means. It's two conflicting thoughts on the same subject, both of which might sound reasonable.
This seems particularly appropriate in the world of Magic. There are opposing thoughts on:
Close-up Magic vs. Big Box Magic
Books vs. Video/DVDs
Amateurs vs. Professionals
The list can go on. In fact, at the very heart of magic is the conflict of two opposing views. Those are "perception and deception." What the spectator perceives should not be the literal truth of the deception, but something else altogether. Antinomy will expound on this basic conflict (and others), sometimes directly in its essays and sometimes indirectly in the way it presents its tricks.
For an online dictionary reference on "Antinomy," go here.